histedit: check first changeset for verb "roll" or "fold" (issue5498) If someone changes "pick" to "roll" or "fold" for the first changeset in a histedit rule Mercurial could remove a wrong changeset if the phase is non-public. roll or fold for the first changeset should be invalid.

encoding: drop circular import by proxying through '<policy>.charencode' I decided not to split charencode.c to new C extension module because it would duplicate binary codes unnecessarily.

policy: reroute proxy modules internally This allows us to split encoding functions from pure.parsers without doing that for cext.parsers. See the next patch for why.