Blender Git Loki

* Layer brush now supports dyntopo.
- To do this I made a little API to make scratch
customdata layers: SCULPT_dyntopo_[ensure/get]_templayer.
Takes a customdata type and a layer name (e.g.
'__dyntopo_bleh") and returns a customdata offset.
- Note that I also did this for the persistent base code.

* Added a macro to check if a tool supports splitting the PBVH
during a stroke, DYNTOPO_HAS_DYNAMIC_SPLIT. It is in sculpt_intern.h
(for now) to avoid the enormous amount of recompiling that is
triggered if DNA_brush_enum.h is modified.

* TODO: Right now the undo code resets original vertex coordinates for
bmesh PBVH. This means tools that rely on original data (sharp and
layer) can't split the pbvh during the stroke, since that will
allocate new undo nodes and reset original coords.

The solution is to move the original data API entirely out of the undo
code.