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
Content-type: text/html; charset={encoding}
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<link rel="icon" href="#url#static/hgicon.png" type="image/png">
<meta name="robots" content="index, nofollow" />
<link rel="stylesheet" href="#url#static/style.css" type="text/css" />