bmesh: optimize bmesh_vert_separate, redice allocs (best cast it wont do any allocs).
gives approx 16% overall speedup to edgesplit modifier.

also reduce size of smallhash stack, was 521, which got doubled and was quite large on the stack. reduce to 64.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56618 954f8c5b-7b00-dc11-b283-0030488c597c