mq: qimporting revision set them to secret

mq: have mq create secret changeset only

wireproto: refuse to lookup secret csets

qclone: ignore local qbase if secret

rebase: only advance phase on successful commit

phases: mechanism to allow extension to alter initial computation of phase This commit add a whennodata list where extension can register a callback to be called if no phase related data are found in the repository. The goal is to ensure the existing extension that move phase data in 2.1 can compute consistent phase boundary for existing repo.

qclone: add a few comment and blank line This help readability.

mq: turn changeset draft on qfinish (except if qparent is secret) As mq automatically sets changesets as secret, it should make them draft when he is done with it. We do not move them automatically to draft when we detect that something else have also set them as secret through their parents.

config: have a way to backup and restore value in config This is introduce to allow temporary overwriting of a config value while being able to reinstall the old value once done. The main advantage over using ``config`` and ``setconfig`` is that backup and restore will properly restore the lack of any config. Restoring the fact that there was no value is important to allow config user to keep using meaniful default value. A more naive approach will result in the following scenario:: Before: config(section, item, my_default) --> my_default temporal overwrite old = config(section, item) … setconfig(section, item, old) After config(section, item, my_default) --> None The first user of this feature should be mq to overwriting minimal phase of future commit.

graft: add test to check the phase of new changesets Graft actually do not keep the phase of the source changesets: no need to change the graft code and add test to check this behaviour.