rewind: default to rewinding the current stack

rewing: add the ability to rewind "from" revisions

evolve: exclude "identical" precursors from the precursors set I'm not sure it is the right thing to do, but it simply thing a lot for now. Otherwise, using 'precursors' to find rewind direction become too complex. This is going to give problematic result in case of prune. Since there are no other precursors to follow.

rewind: move revision selection into its own function This will help making the logic more advanced.

rewind: automatically rewind entire stack We now rewind the full stack, avoiding creating orphans. A `--exact` flag is added to force rewinding only the explicitly specified changesets.

rewind: add a test about rewinding top of stack For now this rewind is creating an orphan. We add the test to check the behavior in that case.

rewind: use rewinded parent when creating multiple changesets Use use the rewinded parent instead of creating orphans based on identical, but obsolete, changesets.

rewind: add a test for rewinding a fold The code already have basic support for case. However the result create orphan that will need to be improved. However, we keep this changeset simple.

rewind: add a test for rewinding a split There are no code change needed but it is worth testing on its own.

rewind: update the working copy if it gets obsoleted If the working copy parent is rewinded, follow the rewind.