rebase: clear updatestate during rebase --abort in more cases
Previously, rebase --abort would only call update if you were on a node that had
already been rebased. This meant that if the rebase failed during the rebase of
the first commit, the working copy would be left dirty (with a .hg/updatestate
file) and rebase --abort would not have update to clean it up.
The fix is to also perform an update if you're still on the target node or on
the original working copy node (since the working copy may be dirty, we still
need to do the update). We don't want to perform an update in all cases though
because of issue4009.
A subsequent patch makes this case much more common, since it causes the entire
rebase transaction to rollback during unexpected exceptions. This causes the
existing test-rebase-abort.t to cover this case.