tree acbfe40614d2330cf5cc5e38464c43b6df1bbd34
parent deb85f46efcba5fea624ee89daea8144abd77c54
author Jason Rhinelander <jason@imaginary.ca> 1492715360 -0400
committer Jason Rhinelander <jason@imaginary.ca> 1493298761 -0400

Expose more instance management functions

This breaks up the instance management functions in class_support.h a
little bit so that other pybind11 code can use it.  In particular:

- added make_new_instance() which does what pybind11_object_new does,
  but also allows instance allocation without `value` allocation.  This
  lets `cast.h` use the same instance allocation rather than having its
  own separate implementation.
- instance registration is now moved to a
  `register_instance()`/deregister_instance()` pair (rather than having
  individual code add or remove things from `registered_instances`
  directory).
- clear_instance() does everything `pybind11_object_dealloc()` needs
  except for the deallocation; this is helpful for factory construction
  which needs to be able to replace the internals of an instance without
  deallocating it.
- clear_instance() now also calls `dealloc` when `holder_constructed`
  is true, even if `value` is false.  This can happen in factory
  construction when the pointer is moved from one instance to another,
  but the holder itself is only copied (i.e. for a shared_ptr holder).