rebase: preserve working copy when redoing in-mem rebase on disk
When in-memory rebase runs into conflicts, we retry it on disk. But
before we do that, we abort the in-memory rebase. That is done because
even though it's mostly in memory, there are still a few state files
written (e.g. the merge state). We should make it not write those
files so we don't need to abort, but for the stable branch, let's
explicitly clear the state we need to clear instead of running the
usual abort code.
Differential Revision: https://phab.mercurial-scm.org/D5356
(binary:application/octet-stream)