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.
Content-type: text/xml
<rss version="2.0">
<channel>
<link>#url#</link>
<language>en-us</language>