fix handling of multiple Content-type headers
This can happen if an error happens while sending
application/mercurial-0.1 content. The error page will
be sent resulting (for at least lighttpd) in the following
headers:
Content-type: application/mercurial-0.1
Content-type: text/html
which result in req.proto = 'application/mercurial-0.1, text/html'
fix issue344
#motd#
<div class="logo">
powered by<br/>
<a href="http://www.selenic.com/mercurial/">mercurial</a>
</div>
</body>
</html>