topics: take locks and start transaction before calling _changetopics This will help us in calling _changetopics in other transactions which already started. Currently the _changetopics creates its own transaction and hence can't be used it a same transaction with any other function or logic.

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.