Merge keying node from tomato branch into trunk.
It was considered stable and helpful by Mango team and it'll help
studio pipeline, because nodes would stop disappearing when opening
files in current trunk.
Full information about keying nodes could be found there:
http://wiki.blender.org/index.php/User:Nazg-gul/Keying
Seems to give quite noticeable speedup, but there's sometimes strange artifacts
showing as darker lines placed in along some kind of tiles.
Not sure what causes them yet.
- Replace FastGaussian blur with GaussianBokeh blur which should give better results.
- Changes a bit formula of saturation which in some cases gives better result.
Also included (commented out) original formula which was also checked by Brecht
and which gave better result in some other cases.
- Made clipping white/black temporal dependent, so hopefully it wouldn't destroy
gradients on edges.