merge of...

merge of 1752145,1753498,1753541,1754129,1754414,1754534,1755323,1756844,1757524,1757534,1757540 from trunk

mod_http2: backport of latest changes
 - intermediate responses
 - graceful shutdown of connections
 - ht debug draft update



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1757542 13f79535-47bb-0310-9956-ffa450edef68