revert: add support for reverting subrepos Reverting a subrepo is done by updating it to the revision that is selected on the parent repo .hgsubstate file. * ISSUES/TODO: - reverting added and removed subrepos is not supported yet. - reverting subrepos is only supported if the --no-backup flag is used (this limitation will be removed on another patch). - The behavior of the --all flag has been changed. It now reverts subrepos as well. Note that this may lead to data loss if the user has a dirty subrepo.