Blender Git Loki

Fix for collapse-edges crash in dyntopo

Was incorrectly testing for a vertex in a set with BLI_ghash_lookup
rather than BLI_ghash_haskey; the key in this case is always null so
the test failed.

This could leave the PBVH in an inconsistent state, since the
top-level map of BMesh vertices to PBVH nodes would indicate the
vertex was in a node, but that node wouldn't actually have any faces
using the vertex. That inconsistent state would eventually lead to a
crash in pbvh_bmesh_vert_remove().

Fixes
http://projects.blender.org/tracker/?func=detail&atid=498&aid=34370&group_id=9