Blender Git Loki

Dyntopo:

* Actually check if normal recalculation flags exists and set it when
splitting nodes in dyntopo. Right now, nodes that need GPU buffer update
will always get in the list to get their normals generated, but to avoid
a possible future breakage better do it right now.
* Avoid keeping deleted/removed vertices in vertex-to-node and unique
vertex hashes, since some checks rely on those and may go awry if these
still exist. Also they pollute the hashes, and may hurt performance
somewhat.