Blender Git Loki

Bugfix:

Previous versions of Blender allowed Vertex Groups to be nameless, which
shouldn't be allowed. This caused problems with rigs from previous versions of Blender being loaded in 2.43+ versions, as the new VGroup feature for the
Armature modifier mis-identified these nameless group(s) as being the Vertex Group
to be used. As well as the checks done when renaming VGroups (from another commit), files created prior to and in 2.43 will have all such groups given default
names.

Code notes:
* I've moved the unique_vertexgroup_name function from src to blenkernel like for
constraints
* Formatting in deform.c tidied up a bit