hghave: add some official category for known-bad and missing-good output
This will make it simple to tag output that are expected to changes. A simple
hghave integration seems enough but smarter behavior around these seems possible
in the future.
Differential Revision: https://phab.mercurial-scm.org/D9607
#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: