Blender Git Loki

Redesigned the EdgeSplit modifier's splitting algorithm to be better
structured and more maintainable. The old algorithm could leave the mesh in an
inconsistent state during recursive calls, making it quite fragile. The new
algorithm keeps the mesh in a consistent state, and should be more robust.

This commit fixes the issues EdgeSplit was having with non-manifold meshes
(bug #4946, also reported by several other people). EdgeSplit now works
correctly with all the test files I have.

This commit also fixes the BLI_ghash_remove function to correctly decrement
gh->nentries (the number of entries in the hashtable) on a successful removal.