Blender Git Loki

Fix possibly wrong matching of tree-view item buttons

The UI code to ensure consistent button state over redraws was just comparing
the name of the item, ignoring the parent names. So with multiple items of the
same name, there might have been glitches (didn't see any myself though).

There's a leftover to-do though, we don't check yet if the matched buttons are
actually from the same tree. Added TODO comment.