new ap_is_allowed_protocol() for testing configured protocols, added H2Upgrade...

new ap_is_allowed_protocol() for testing configured protocols, added H2Upgrade on/off directive, changed H2Direct default back to on when h2c is in Protocols

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1709587 13f79535-47bb-0310-9956-ffa450edef68