Merged /httpd/httpd/trunk:r1864924,1868506,1868654,1868927 from trunk

Merged /httpd/httpd/trunk:r1864924,1868506,1868654,1868927 from trunk

  *) mod_md: Adding the several new features.
     The module offers an implementation of OCSP Stapling that can replace fully or
     for a limited set of domains the existing one from mod_ssl. OCSP handling
     is part of mod_md's monitoring and message notifications. If can be used
     for sites that do not have ACME certificates.
     The url for a CTLog Monitor can be configured. It is used in the server-status
     to link to the external status page of a certicate.
     The MDMessageCmd is called with argument "installed" when a new certificate
     has been activated on server restart/reload. This allows for processing of
     the new certificate, for example to applications that require it in different
     locations or formats.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1868930 13f79535-47bb-0310-9956-ffa450edef68