On the 2.4.x branch: merge of r1701609-1705681 from trunk.

  *) mod_http2: streaming of request output now reacts timely to data
     from other streams becoming available. Same for new incoming requests.
 


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1778629 13f79535-47bb-0310-9956-ffa450edef68