Merge of r1747550 from trunk:

mod_proxy_http2 no longer shares objects with mod_http2
h2_casecmpstr eliminated, uses backported ap_cstr_casecmp*



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1748359 13f79535-47bb-0310-9956-ffa450edef68