mq: use dirstateguard instead of dirstate.invalidate (qrefresh) Before this patch, "mq.queue.refresh()" uses "dirstate.invalidate()" as a kind of "restore .hg/dirstate to the original status" during a failure. But it just discards changes in memory, and doesn't actually restore ".hg/dirstate". Then, it can't work as expected, if "dirstate.write()" is executed while processing. This patch uses "dirstateguard" instead of "dirstate.invalidate()" to restore ".hg/dirstate" during a failure even if "dirstate.write()" is executed before a failure. This patch also removes "beginparentchage()" and "endparentchange()", because "dirstateguard" makes them useless. This is a part of preparations to fix the issue that the recent (in memory) dirstate isn't visible to external processes (e.g. "precommit" hook).