phase: say "Returns 0" instead of "Return 0" like other command help

dirstate: remove double imports of errno

cmdserver: mask return code of runcommand in the same way as dispatch.run "hg help" does not state that the code for abort is 255, but it's confusing to have different code between hg command and command server. Tests of python-hglib 1.2 passed with this change.

cmdserver: include non-zero return code of runcommand in test output

cmdserver: recreate mq object on runcommand in case queue path was changed repo.mq needs to be recreated after queue path change. Since there is little benefit to keep invalidated mq object, it always delete repo.mq.

cmdserver: reload mq on each runcommand request to avoid corruption If mq was changed by another process, command server should invalidate caches. Otherwise, mq status would go wrong.

localrepo: add hook point to invalidate everything on each command-server run MQ extension will wrap this function to invalidate its state. repo.invalidate cannot be wrapped for this purpose because qpush obtains repo.lock in the middle of the operation, triggering repo.invalidate. Also, it seems wrong to obtain lock earlier because mq data is non-store parts.