new Protocols directive and core API changes to enable protocol switching on...

new Protocols directive and core API changes to enable protocol switching on HTTP Upgrade or ALPN, implemented in mod_ssl and mod_h2

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1692486 13f79535-47bb-0310-9956-ffa450edef68