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 zh_CN
checking for parse errors