Add a multi-repository server
This merges a bunch of the ideas for a multi-repository CGI script and
simplifies things a bit.
It uses PATH_INFO so it generally wants paths of the form:
http://host/hg.cgi/virtualpath
This gets mapped via a simple config file to the real path. All info
about the repo is read from the repo's hgrc.
#header#
<title>#repo|escape#: #file# history</title>
<description>#file# revision history</description>
#entries#
</channel>
</rss>