Blender Git Loki

Fix #29367: Vertex parent regression

Regression was introduced in svn rev40343. It was caused by re-creating
EditMesh structure which was needed to solve issues with parenting to
vertices after topology changes. This would also erase derivedMesh.

Problem reported now is caused by missing derivedMesh which is used
to solve parenting and apply inverted matrix on ob->parentin, so
parented object used to stay at exactly the same position it used to
stay before parenting.

Not very nice solving of this issue: re-create derivedMesh after
re-creating EditMesh when parenting. Nicer solution would require
bigger changes and probably ful lrefactor of this tools.