Blender Git Loki

Deleting keyframes usability tweak:
There won't be dangling "empty" actions left behind anymore in the
DopeSheet channel list after you've deleted all their keyframes (and
don't want to add keyframes to them anymore).

Of course, this poses problems with more actions getting created if
you then go and keyframe those objects again. If this does turn out to
be an equally bad problem, then another approach from the channel
filtering code side (probably aided by the restructed code) will help
(though doesn't solve the problem where people complain of having
heaps of "empty" actions dangling from objects they no longer want
animated).