zsh_completion: handle --rev as well as -r for diff and revert
Completion for hg diff and revert should suggest all files in context of a
non-current revision. The script used to look only for `-r foo`, and now it
also understands `--rev foo`.
Differential Revision: https://phab.mercurial-scm.org/D4427
#require docutils gettext
$ $TESTDIR/check-gendoc de
checking for parse errors
Die Dateien werden dem Projektarchiv beim n\xc3\xa4chsten \xc3\x9cbernehmen (commit) hinzugef\xc3\xbcgt. Um dies vorher r\xc3\xbcckg\xc3\xa4ngig zu machen, siehe:hg:`forget`. (esc)
warning: please have a space before :hg: