- making local object data - Curve/Mesh/MBall lost references to linked materials.
- joining a linked mesh object into a local one lost the link.
As well as these reported bugs, checked all local functions for consistency/correctness and found other cases which would also fail.
- making local metaball didn't ensure unique ID name.
- make_local_armature() was missing check for object users - main body of code would never run.
- local particles didn't set the dupli-group or textures to extern.
checked all local functions for consistency/correctness.