rebase: don't try to prune obsolete changeset already in the destination
With similar motivations to the previous changesets, we stop marking changeset
from pruning when it is not the command intention. In this case, we still need
to distinguish between the strip and the obsolete case.
histedit: don't cleanup nodes already disposed of
If something else took care of these temporary nodes, we don't need to do
anything about it. This less liberal usage of pruning through cleanup nodes
will help us further cleanup on the road to explicitly tracks folds.