Blender Git Loki

Fix wrong proxy pointer hanging around after making all local

The issue was caused because of the following circumstances:

- Making All Local will just iterate all IDs and clear linked flags
- It will not do anything with objects which are already local (and
since proxy rig is local nothing will be changing it).

This commit makes it so id_clear_lib_data() takes care of clearing
all related proxy pointers, avoiding situations when proxy rig will
point to a local armature.

Reviewers: campbellbarton

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D1276