Fails --- next commit will tighten test.

Non-contiguous arrays

Add and declare to Python functions

    double_mat_cm() --- compute 2* a column-major matrix
    double_mat_rm() --- compute 2* a row-major matrix

to 'eigen.cpp' tests / example.

In eigen.h, type_caster<Type>::load():  For the 'ndim == 1' case, use
the 'InnerStride' type because there is only an inner stride for a
vector.  Choose between (n_elts x 1) or (1 x n_elts) according to
whether we're constructing a Vector or a RowVector.

Passing a non-contiguous one-dimensional numpy array gives incorrect
results, so three of these tests fail.  The only one passing is the
simple case where the numpy array is contiguous and we are building a
column-major vector.  Subsequent commit will fix the three failing
cases.

Fix test diff output under python2.7

PR #220 broke failed test output under python2.7, which doesn't support
the keepends argument to splitlines.

More informative error message when `py::make_tuple` fails

Allow std::enable_shared_from_this when using const element type

Allows const types to be used by shared_ptr

Added warning about same-address-optimization

See https://github.com/pybind/pybind11/issues/254

Use prefix increment in make_iterator

Add callback examples with named parameters

Allow pybind11::arg to have 0, false, or "" as default values.

Skip FindPythonLibsNew if PYTHONLIBS_FOUND is defined (fix #236)