mod_proxy_http: Don't expect the backend to ack the "Connection: close" to

finally close those not meant to be kept alive by SetEnv proxy-nokeepalive
or force-proxy-request-1.0, and respond with 502 instead of 400 if its
Connection header is invalid.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1658760 13f79535-47bb-0310-9956-ffa450edef68