upgrade: clearly list optimisations This makes the command operation clearer. And this will be necessary to have a short version of this information with the next changesets, teaching `hg debugupgraderepo` about `--quiet`. Differential Revision: https://phab.mercurial-scm.org/D8428

nodemap: move the mode option to storage.revlog.nodemap.mode The option stay experimental as long as the main feature is. Differential Revision: https://phab.mercurial-scm.org/D8422