Apparently with homebrew the correct package for python3 is now just
`python`; python 2 was relegated to 'python@2', and `python3` is an
alias for `python` (which needs to be upgraded rather than installed).

This fixes the test code on big-endian architectures: the array support
(PR #832) had hard-coded the little-endian '<' but we need to use '>' on
big-endian architectures.

This function already has a `using namespace detail`, so all the
`detail::` qualifications are not needed.

This updates the `py::init` constructors to only use brace
initialization for aggregate initiailization if there is no constructor
with the given arguments.

This, in particular, fixes the regression in #1247 where the presence of
a `std::initializer_list<T>` constructor started being invoked for
constructor invocations in 2.2 even when there was a specific
constructor of the desired type.

The added test case demonstrates: without this change, it fails to
compile because the `.def(py::init<std::vector<int>>())` constructor
tries to invoke the `T(std::initializer_list<std::vector<int>>)`
constructor rather than the `T(std::vector<int>)` constructor.

By only using `new T{...}`-style construction when a `T(...)`
constructor doesn't exist, we should bypass this by while still allowing
`py::init<...>` to be used for aggregate type initialization (since such
types, by definition, don't have a user-declared constructor).

* Fix segfault when reloading interpreter with external modules

When embedding the interpreter and loading external modules in that
embedded interpreter, the external module correctly shares its
internals_ptr with the one in the embedded interpreter.  When the
interpreter is shut down, however, only the `internals_ptr` local to
the embedded code is actually reset to nullptr: the external module
remains set.

The result is that loading an external pybind11 module, letting the
interpreter go through a finalize/initialize, then attempting to use
something in the external module fails because this external module is
still trying to use the old (destroyed) internals.  This causes
undefined behaviour (typically a segfault).

This commit fixes it by adding a level of indirection in the internals
path, converting the local internals variable to `internals **` instead
of `internals *`.  With this change, we can detect a stale internals
pointer and reload the internals pointer (either from a capsule or by
creating a new internals instance).

(No issue number: this was reported on gitter by @henryiii and @aoloe).

Fix return from `std::map` bindings to `__delitem__`: we should be returning `void`, not an iterator.

Also adds a test for map item deletion.

Found via `codespell`

The anonymous struct nested in a union triggers a -Wnested-anon-type
warning ("anonymous types declared in an anonymous union are an
extension") under clang (#1204).  This names the struct and defines it
out of the definition of `instance` to get around to warning (and makes
the code slightly simpler).

- UPDATEIFCOPY is deprecated, replaced with similar (but not identical)
  WRITEBACKIFCOPY; trying to access the flag causes a deprecation
  warning under numpy 1.14, so just check the new flag there.
- Numpy `repr` formatting of floats changed in 1.14.0 to `[1., 2., 3.]`
  instead of the pre-1.14 `[ 1.,  2.,  3.]`.  Updated the tests to
  check for equality with the `repr(...)` value rather than the
  hard-coded (and now version-dependent) string representation.

PEP8 indicates (correctly, IMO) that when an annotation is present, the
signature should include spaces around the equal sign, i.e.

    def f(x: int = 1): ...

instead of

    def f(x: int=1): ...

(in the latter case the equal appears to bind to the type, not to the
argument).

pybind11 signatures always includes a type annotation so we can always
add the spaces.

* Make register_dtype() accept any field containers

* Add a test for programmatic dtype registration

When using the mixed position + vararg path, pybind over inc_ref's
the vararg positions. Printing the ref_count() of `item` before
and after this change you see:

Before change:

```
refcount of item before assign 3
refcount of item after assign 5
```

After change
```
refcount of item before assign 3
refcount of item after assign 4
```

The `py::args` or `py::kwargs` arguments aren't properly referenced
when added to the function_call arguments list: their reference counts
drop to zero if the first (non-converting) function call fails, which
means they might be cleaned up before the second pass call runs.

This commit adds a couple of extra `object`s to the `function_call`
where we can stash a reference to them when needed to tie their
lifetime to the function_call object's lifetime.

(Credit to YannickJadoul for catching and proposing a fix in #1223).

In the latest MSVC in C++17 mode including Eigen causes warnings:

    warning C4996: 'std::unary_negate<_Fn>': warning STL4008: std::not1(),
    std::not2(), std::unary_negate, and std::binary_negate are deprecated in
    C++17. They are superseded by std::not_fn(). You can define
    _SILENCE_CXX17_NEGATORS_DEPRECATION_WARNING or
    _SILENCE_ALL_CXX17_DEPRECATION_WARNINGS to acknowledge that you have
    received this warning.

This disables 4996 for the Eigen includes.

Catch generates a similar warning for std::uncaught_exception, so
disable the warning there, too.

In both cases this is temporary; we can (and should) remove the warnings
disabling once new upstream versions of Eigen and Catch are available
that address the warning. (The Catch one, in particular, looks to be
fixed in upstream master, so will probably be fixed in the next (2.0.2)
release).

Pybind11's default conversion to int always produces a long on Python 2 (`int`s and `long`s were unified in Python 3). This patch fixes `int` handling to match Python 2 on Python 2; for short types (`size_t` or smaller), the number will be returned as an `int` if possible, otherwise `long`. Requires Python 2.5+.

This is needed for things like `sys.exit`, which refuse to accept a `long`.

None of the three currently recommended approaches works on PyPy, due to
it not garbage collecting things when you want it to. Added a note with
example showing how to get interpreter shutdown callbacks using the Python
atexit module.

This changes the travis-ci eigen download code to extract the tar on the
fly (rather than saving to a file first), and extracts into an `eigen`
directory rather than using upstream's `eigen-eigen-xxxxx` directory.

This also bumps the travis-ci eigen release to 3.3.4, in an attempt to
see if it fixed the -Wdeprecated warnings (it did not); the build setup
cleanup seems worth committing anyway.

This commit turns on `-Wdeprecated` in the test suite and fixes several
associated deprecation warnings that show up as a result:

- in C++17 `static constexpr` members are implicitly inline; our
  redeclaration (needed for C++11/14) is deprecated in C++17.

- various test suite classes have destructors and rely on implicit copy
  constructors, but implicit copy constructor definitions when a
  user-declared destructor is present was deprecated in C++11.

- Eigen also has various implicit copy constructors, so just disable
  `-Wdeprecated` in `eigen.h`.

py::class_<T>'s `def_property` and `def_property_static` can now take a
`nullptr` as the getter to allow a write-only property to be established
(mirroring Python's `property()` built-in when `None` is given for the
getter).

This also updates properties to use the new nullptr constructor internally.

A few fixes related to how we set `__qualname__` and how we show the
type name in function signatures:

- `__qualname__` isn't supposed to have the module name at the
beginning, but we've been putting it there.  This removes it, while
keeping the `Nested.Class` name chaining.

- print `__module__.__qualname__` rather than `type->tp_name`; the
latter doesn't work properly for nested classes, so we would get
`module.B` rather than `module.A.B` for a class `B` with parent `A`.
This also unifies the Python 3 and PyPy code.  Fixes #1166.

- This now sets a `__qualname__` attribute on the type (as would happen
in Python 3.3+) for Python <3.3, including PyPy.  While not particularly
important to have in earlier Python versions, it's useful for us to be
able to extracted the nested name, which is why `__qualname__` was
invented in the first place.

- Added tests for the above.

Non-user facing. 
Found using `codespell -q 3`

The just-updated flake8 package hits a bunch of:

    E741 ambiguous variable name 'l'

warnings.  This commit renames them all from `l` to `lst` (they are all
list values) to avoid the error.

- For the debian/buster docker build (GCC 7/C++17) install and use the
  system `catch` package; this also renames "COMPILER_PACKAGES" to
  "EXTRA_PACKAGES" since it now contains a non-compiler package.

- Add a status message indicating the catch version being used for
  compiling the embedded tests

- Simplify some bash code by using VAR+=" foo" to append (rather than
  VAR="${VAR} foo"

- Fix CMAKE_INCLUDE_PATH appending: it was prepending the ':' but not
  the existing $CMAKE_INCLUDE_PATH value and so would end up with
  ":/eigen-path" if CMAKE_INCLUDE_PATH was already set.  (This wasn't
  bug that was actually noticed since currently nothing else sets it).

Building with the (VS2017) /permissive- flag puts the compiler into
stricter standards-compliant mode.  It shouldn't cause the compiler to
work differently--it just disallows some non-conforming code--so should
be perfectly fine for the test suite under all VS2017 builds.

This commit also fixes one failure under non-permissive mode.

This fixes a bug introduced in b68959e8
when passing in a two-dimensional, but conformable, array as the value
for a compile-time Eigen vector (such as VectorXd or RowVectorXd).  The
commit switched to using numpy to copy into the eigen data, but this
broke the described case because numpy refuses to broadcast a (N,1)
into a (N).

This commit fixes it by squeezing the input array whenever the output
array is 1-dimensional, which will let the problematic case through.
(This shouldn't squeeze inappropriately as dimension compatibility is
already checked for conformability before getting to the copy code).

When using `method_adaptor` (usually implicitly via a `cl.def("f",
&D::f)`) a compilation failure results if `f` is actually a method of
an inaccessible base class made public via `using`, such as:

    class B { public: void f() {} };
    class D : private B { public: using B::f; };

pybind deduces `&D::f` as a `B` member function pointer.  Since the base
class is inaccessible, the cast in `method_adaptor` from a base class
member function pointer to derived class member function pointer isn't
valid, and a cast failure results.

This was sort of a regression in 2.2, which introduced `method_adaptor`
to do the expected thing when the base class *is* accessible.  It wasn't
actually something that *worked* in 2.1, though: you wouldn't get a
compile-time failure, but the method was not callable (because the `D *`
couldn't be cast to a `B *` because of the access restriction).  As a
result, you'd simply get a run-time failure if you ever tried to call
the function (this is what #855 fixed).

Thus the change in 2.2 essentially promoted a run-time failure to a
compile-time failure, so isn't really a regression.

This commit simply adds a `static_assert` with an accessible-base-class
check so that, rather than just a cryptic cast failure, you get
something more informative (along with a suggestion for a workaround).

The workaround is to use a lambda, e.g.:

    class Derived : private Base {
    public:
        using Base::f;
    };

    // In binding code:
    //cl.def("f", &Derived::f); // fails: &Derived::f is actually a base
                                // class member function pointer
    cl.def("f", [](Derived &self) { return self.f(); });

This is a bit of a nuissance (especially if there are a bunch of
arguments to forward), but I don't really see another solution.

Fixes #1124