Blender Git Loki

Merge branch 'master' into temp_bmesh_multires
Also:

* added BMLog function to save mesh IDs.
- Used by SCULPT_UNDO_DYNTOPO_BEGIN/END instead of
saving the whole mesh, which was the previous behavior.
* SCULPT_UNDO_DYNTOPO_BEGIN no longer pushes a non-dyntopo
geomtry undo node, as this is no longer necassary.

This greatly speeds up going into/out of sculpt mode
with dyntopo enabled, as before it was copying
the mesh twice.