Check for parent/mod as well as parent.mod in findext.
Debian/Ubuntu ship a system-wide hgrc that loads extensions using
the syntax hgext/extension=, rather than hgext.extension=. Although
the extensions work correctly, hg help <extension> doesn't
understand this form without this patch.
#header#
<title>#repo|escape#: #file|escape# history</title>
<description>#file|escape# revision history</description>
#entries%filelogentry#
</channel>
</rss>