rebase: properly abort when destination is public (issue4896)
After rebasing a set of changes onto a public changeset and having the first one
be skipped, if you try to abort, the operation fails. This fix adds a check to
disallow the target rev into the dstates list within the abort function. This
list is checked for immutable states before the rest of abort does its thing.
(binary:application/octet-stream)