shortest: fix an off-by-1 when disambiguating against revnums
Revision "5" is an unambiguous hex prefix in a repo with 5 revisions;
it's only "4" and lower that are ambiguous.
Differential Revision: https://phab.mercurial-scm.org/D4420
#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: