strip: move checksubstate from mq to strip One more step for issue3824

mq: prepare a strip extension for extraction Strip will lives in its own extension. The extension is surprisingly called `strip`. (as discussed in issue3824) The `mq` extension force the use of the strip extension when its enabled. This will both necessary for backward compatibility (people expect `mq` to comes with strip) and become some utility function used by `mq` will move in the strip extension.

histedit: remove unused parents() call

mq: have the strip command functionnal on repo without mq This is the last step before being able to extract `strip` in its own extension. The changes are made in mq to allow a move only extraction without touching a line of code.

mq: extract `mq.queue.strip` It does not depend on `mq.queue` anymore.

mq: drop the use of mq.queue.qparent in mq.queue.strip Same as in the previous changeset, rev is never `None`. We can just copy the two relevant lines in in `queue.strip`. This help having `queue.strip` independent from `queue`. One further step toward the extraction of `strip` in an independent extension. (As discussed in issue3824).

mq: drop the use of mq.queue.qparent in mq.strip In this case, rev is never `None`. We can just copy the two relevant lines in in `strip`. This help having `strip` independent from `queue` one further step toward its extraction in an independent extension. (As discussed in issue3824).

mq: document repo.mq.qparents The function is not very complex but writing this doc helped me to check if I got everything right.

mq: use the new checklocalchange in the strip command The strip command never use the `refresh` argument. So we can use the function we just extracted.

mq: extract checklocalchanges from `mq.queue` The core part of `checklocalchanges` is now mq independent. We can extract it in a standalone function to help the extraction of `strip` as discussed in issue3824. A `checklocalchanges` function stay in `mq.queue` with the part related to "refresh first" messages.