Blender Git Loki

Bugfix [#25831] Sorting channels broken

Recoded animation channel sorting code. In particular, the old code
didn't handle "islands" of selected items well (i.e. a chain of
several connected items in a row), with some of these cases having
unpredictable results.

There were also some bugs in the way some of the rearranging methods
worked, allowing some invalid operations to be performed. Some of
these probably triggered errors such as some channels getting stuck,
and so on.