Merge of r1757985,r1758003 from trunk

mod_http2: fixed bug in stream shutdown, support for nghttp2 invalid header callback from 1.14.0 and onwards.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1758011 13f79535-47bb-0310-9956-ffa450edef68