Fixed incorrect use of r->http_version in scgi module.

Fixed incorrect use of r->http_version in scgi module.

The r->http_version is a version of client's request, and modules must
not set it unless they are really willing to downgrade protocol version
used for a response (i.e. to HTTP/0.9 if no response headers are available).
In neither case r->http_version may be upgraded.

The former code downgraded response from HTTP/1.1 to HTTP/1.0 for no reason,
causing various problems (see ticket #66).  It was also possible that
HTTP/0.9 requests were upgraded to HTTP/1.0.