Blender Git Loki

Assorted animsys fixes/tweaks:

* Fixed all the dangerous code added in 27907. Using the code there, scripters could corrupt animation files in ways which would render them useless, with channels not appearing in any animation editors, and others not getting evaluated at all.

* Partial fix of bug 21818, by disabling destructive replacement of keyframes. Will followup this commit with a more comprehensive commit which gets rid of the rest of the problems, by incorporating some requests from Durian team.

* Fixed problems with users being able to see+edit the name of the active Keying Set in the Scene buttons. There is still a bug though with the list widget given how the indices are now interpreted...