Blender Git Loki

Fix for weight painting errors, as reported by Bassam.

- Undo/Redo didn't work
- Crash on using weightpaint with Armature-modifier (instead of parent).

Note: checking if an object is being deformed cannot be simply done with
checking for a parent anymore... for this a call in modifier.c has been
added; modifiers_isDeformedByArmature(Object *). It even returns the
Armature object pointer.