Blender Git Loki

Action Layer Up/Down: Fixes for NLA Solo / NLA Muting

Now marking NLA Tracks as Solo'd and muting the NLA stack are linked together
when using the Action Layer Up/Down tools. That is, when switching from a NLA strip
to the active action, if the track was solo'd, then the NLA stack will get muted;
and when switching from the active action to a NLA track, if the stack was muted,
the track will get solo'd. This linkage means that we ensure that when moving up
and down the stack, we can continue to check the actions in isolation without things
messing up when you switch to and from the active action.

Also fixed a bug where this wasn't getting applied when going in the other direction.

TODO:
- When we get the rest/reference track support, we're going to need to insert
some calls to flush the restpose values so that values from the previously
used action do not pollute the pose for the new action (if not all the
same controls get keyed across both). For now, it's best to only do this
switching from the first frame.