* Adding test_class_sh_disowning.
* Fixing minor namespace naming inconsistency between test_class_sh_*.cpp files.
* Replacing py::overload_cast with plain cast for C++11 compatibility.
* Accommodate that the C++ order of evaluation of function arguments is unspecified.
* Adaption of PyCLIF virtual_py_cpp_mix test.
* Removing ValueError: Ownership of instance with virtual overrides in Python cannot be transferred to C++. TODO: static_assert alias class needs to inherit from virtual_overrider_self_life_support.
* Bringing back ValueError: "... instance cannot safely be transferred to C++.", but based on dynamic_cast<AliasType>.
* Fixing oversight: adding test_class_sh_virtual_py_cpp_mix.cpp to cmake file.
* clang <= 3.6 compatibility.
* Fixing oversight: dynamic_raw_ptr_cast_if_possible needs special handling for To = void. Adding corresponding missing test in test_class_sh_virtual_py_cpp_mix. Moving dynamic_raw_ptr_cast_if_possible to separate header.
* Changing py::detail::virtual_overrider_self_life_support to py::virtual_overrider_self_life_support.
* Initial version of virtual_overrider_self_life_support (enables safely passing unique_ptr to C++).
* Clang 3.6, 3.7 compatibility.
* Adding missing default constructor.
* Restoring test for exception for the case that virtual_overrider_self_life_support is not used.
* Fixing oversight: Adding missing holder().ensure_was_not_disowned().
* Adding unit tests for new `struct smart_holder` member functions.
* Moving virtual_overrider_self_life_support to separate include file, with iwyu cleanup.
