Backport yet another security fix; if stream_cl exceeds the 'stated' 
  CL which proxy_request_body asked us to send, then we have to quit 
  forwarding any more bytes (we won't even pass the header if we 
  hadn't yet.)

  Closes an HTTP Request splitting edge case.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/proxy-reqbody-2.0.x@230722 13f79535-47bb-0310-9956-ffa450edef68