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>Mercurial repositories index</title>
</head>
<body>
<h2>Mercurial Repositories</h2>
The specified repository "#repo|escape#" is unknown, sorry.
Please go back to the main repository list page.
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