hghave: check darcs version more strictly
test-convert-darcs.t suddenly started failing on my Debian sid machine. The
reason was Darcs was upgraded from 2.12.0 to 2.12.4 so the original pattern
got to match the last two digits. Fix the pattern to match 2.2+.
#require docutils gettext
$ $TESTDIR/check-gendoc ru
checking for parse errors