mask, also avoid making vertex groups if they will not be filled.
* Add back image pin option in image editor header.
* Fix deep shadow not respecting Cast Buffer Shadows option.
* Tangent space normal map baking should work again now.
* Fix a problem with particle duplis, due to own bugfix for #20350,
the problem for that seems to be in dupliverts, not particles.
* Fix external multires data link getting lost on exiting editmode.
(commits 27776,27777,27830,27840,27841,27862 by Brecht from render25 branch)