Blender Git Loki

Fix some crashes when ID would reference itself.

Typical case: bones having constraints targetting other bones from same
armature. ID swap needs remapping here.

Really have to find something better than regular ID copy + swap + relinking
for override operations, this is horribly inneficient, complicated
and... most likely a nest of bugs and worms.

(pretty sure e.g. we still can generate same pointers during writefile
with current code :( ).