Blender Git Loki

Hack to workaround scene update lock caused by GIL

Couple of RNA callbacks would imply scene update routines
to trigger. This works fine for until some objects does have
drivers.

If some object does have driver, it'll try to lock GIL
when evaluating this driver, and GIL is already locked by
a python API, which causes deadlock.

For now made it so RNA callbacks doesn't do threaded update.
This is not so much nice, especially since Cycles might
use the same API for motion blur, but for now don't see
better way to solve the deadlock.