Blender Git Loki

Some versioning changes/patching of the brush system:

* Change overlay alphas to 33 if not initialized. This should have been
done for 2.67 but better do it now to avoid frustration with overly
transparent overlays. For users that have set this low manually this
will reset the setting to 33 but I think it's less irritating than users
who unwillingly had the setting to 1 and saw nothing when activating the
overlay.

* Allow overlay alpha to be zero as well

* Reset old, now obsolete BRUSH_FIXED flag for brushes that still use
this. I am doing this here to avoid patching hell when the paint brush
is merged, since it's not possible to know the merged version
beforehand, and this flag will be used.