evolve: don't use exception for local flow control The LocalMergeFailure class was added in 3f91654713dd (obsolete Move merge failure handling into stabilize code, 2012-08-20). I think the "if compat.hasconflict(r)" check was added later. Now that we have that check, we should use that for flow control instead. Note that this means that any unexpected exception from _relocatecommit() will now just raise (and roll back the transaction). I think that's an improvement.