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
*** 'a\nc\n\n\n\n' 'a\nb\n\n\n'
*** 'a\nb\nc\n' 'a\nc\n'
*** '' ''
*** 'a\nb\nc' 'a\nb\nc'
*** 'a\nb\nc\nd\n' 'a\nd\n'
*** 'a\nb\nc\nd\n' 'a\nc\ne\n'
*** 'a\nb\nc\n' 'a\nc\n'
*** 'a\n' 'c\na\nb\n'
*** 'a\n' ''
*** 'a\n' 'b\nc\n'
*** 'a\n' 'c\na\n'
*** '' 'adjfkjdjksdhfksj'
*** '' 'ab'
*** '' 'abc'
*** 'a' 'a'
*** 'ab' 'ab'
*** 'abc' 'abc'
*** 'a\n' 'a\n'
*** 'a\nb' 'a\nb'
done