bvh4_builder_fast no longer uses primTy
different builder classes for different leaf types
updates
default constructor of PrimInfo does nothing
no longer using Centroid_Scene_AABB
removed global_bounds
popping last item from stack, increases builder performance
separated workstack, added workheap
updates
compile fix for debug mode
more correct termination criteria for bvh4_builder_fast
bvh4_builder_fast used correct logBlockSize
some bugfixes in spatial splits, still not working properly
bugfix in hair builder