rewriteutil: say how many commits would become orphan if commit is rewritten This copies the message from the evolve extension, but modifies it a bit to work with the grammar (in particular with the use of "change branch of" as `action`). I don't know why it doesn't use the same `_formatrevs()` as for public commmits. Differential Revision: https://phab.mercurial-scm.org/D10671