mod_proxy_http2: own h2_proxy_util.c source file to avoid duplicate use of...

mod_proxy_http2: own h2_proxy_util.c source file to avoid duplicate use of h2_util.c, updated dsp and cmake as well as configure files

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1747550 13f79535-47bb-0310-9956-ffa450edef68