compat: fix instabilities compat
We added an instabilities method for old version of Mercurial. But we returned
an old value for orphan changesets, the one before the big evolve renaming.
Fix the return value to match the new return values.
This software was downloaded from
https://www.mercurial-scm.org/repo/evolve/
Copyright 2011 Peter Arrenbrecht <peter.arrenbrecht@gmail.com>
Logilab SA <contact@logilab.fr>
Pierre-Yves David <pierre-yves.david@ens-lyon.org>
Patrick Mezard <patrick@mezard.eu>
This software may be used and distributed according to the terms of the GNU
General Public License version 2 or any later version.
On Debian systems, the complete text of the GNU General Public License version
2 can be found in `/usr/share/common-licenses/GPL-2'.