static cast handle for rtrn_valu works by simply dropping in code from type_caster_base (marked with comments). rtrn_rref raises a RuntimeError, to be investigated.

static cast handle for rtrn_cref works by simply dropping in code from type_caster_base (marked with comments). rtrn_mref and rtrn_mptr work via const_cast (to add const).

static cast handle for rtrn_cptr works by simply dropping in code from type_caster_base (marked with comments).

Systematically setting mtxt for all rtrn_mpty_* functions (preparation, the values are not actually used yet).

Retrieving smart_holder pointer in type_caster<std::unique_ptr<mpty[ const]>>::load, and using it cast_op operators.

Retrieving smart_holder pointer in type_caster<std::shared_ptr<mpty[ const]>>::load, and using it cast_op operators.

classh.h: renaming of class_ to classh + namespace; forking test_classh_wip from test_type_caster_bare_interface_demo.

Pure copy of `class class_` implementation in pybind11.h (master commit 98f1bbb8).

minor test_private_first_base.cpp simplification (after discovering that this can be wrapped with Boost.Python, using boost::noncopyable)

(This demo does NOT involve smart pointers at all, unlike the otherwise similar test_smart_ptr_private_first_base.)