Blender Git Loki

Constraints UI Tweak:

Experimental tweak for the "Object Constraints" tab so that it now
shows a warning message instead of the "Add Constraints" button when
the active object is in Pose Mode. Hopefully this will further
alleviate any confusion over Object vs Bone level constraints.

Todo:
While coding this, I noticed that we currently don't have any way of
making help-text labels in UI panels which can span multiple lines
(word-wrapped or manually split). Probably not a critical issue, but
it would be nice for completeness...