Blender Git Loki

Action Editor "Browse" Fix: Stash active action if nothing else uses it

Following the initial action management commits for 2.74, blurrymind pointed out a
problematic workflow involving the "Browse Action" dropdown in the Action Editor
which would lead to actions being accidentally lost. Namely, it turns out that
game animators frequently flip between different actions from the Browse menu while
working.

While the new up/down operators and/or other NLA based tools are better suited to this
without the problems of actions getting lost, some additional precautions were needed
for the Browse menu as well. So now, if the active action will have no users as a result
of the switch (i.e. it was a new action, and the user is checking on a previous action
via the Browse menu), this action will now get stashed. This workflow is not perfect though,
as there is the problem of the stashed action strips not reflecting the actions they reference.