Blender Git Loki

NLA SoC: Fixes for Operator Poll Callbacks

* Clicking on NLA tracks while in TweakMode now works so that channels can be muted/protected/expanded as per usual. However, they cannot be selected, as changing the selection state can interfere with TweakMode state changes

* Operators for animation channel-lists now use proper poll callbacks, which also take into account TweakMode where appropriate (i.e. all selection operators are now allowed to operate in NLA while in TweakMode, and all other operators will only work in Animation Editors)

* Action Editor operators now use the poll callback for Action Editors/DopeSheet instead of the generic active-araa one.