Properly handle HTTP versions in pywsgi

There's no way for a WSGI application to discover the HTTP version used in the request, since the WSGIHandler is setting environ["SERVER_PROTOCOL"] to an hard-coded "HTTP/1.0". This patch fixes it, and also makes the server declare support for HTTP/1.1 in its responses, as the specification requires.

Issue https://github.com/surfly/gevent/issues/79 is related, but this patch seems a better fix than the one proposed there.

See also:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.1
http://www.ietf.org/rfc/rfc2145.txt (section 2.3, fourth paragraph)