On the 2.4.x branch: merge of r1776738,1777160,1777324 from trunk

backport of latest mod_http2 related changes.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1777344 13f79535-47bb-0310-9956-ffa450edef68