bmesh speedup for bvh building, replace SmallHash with BLI_bitmap, using a hash doesn't make much sense since in most cases all vertices are accessed and the hash isn't guaranteed to be small.
gives ~9x speedup to filling 'cagecos' in my own tests on a high poly mesh.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56090 954f8c5b-7b00-dc11-b283-0030488c597c