rebase: allow aborting when descendants detected
With this, all aborts will succeed in removing the state, rather than
leaving the user in 'what do I do now?' limbo.
basic:
creating
creating
creating
creating
fakeuncacheable:
creating
creating
creating
creating
creating
creating
repository tip rolled back to revision -1 (undo commit)
working directory now based on revision -1
repository tip rolled back to revision -1 (undo commit)
working directory now based on revision -1
setbeforeget:
0
creating
None