*) core: Adding SSL related inquiry functions to the server API.

  *) core: Adding SSL related inquiry functions to the server API.
     These function are always available, even when no module providing
     SSL is loaded. They provide their own "shadowing" implementation for
     the optional functions of similar name that mod_ssl and impersonators
     of mod_ssl provide.
     This enables loading of several SSL providing modules when all but
     one of them registers itself into the new hooks. Two old-style SSL
     modules will not work, as they replace the others optional functions
     with their own.
     Modules using the old-style optional functions will continue to work
     as core supplies its own versions of those.
     The following has been added so far:
     - ap_ssl_conn_is_ssl() to query if a connection is using SSL.
     - ap_ssl_var_lookup() to query SSL related variables for a
       server/connection/request.
     - Hooks for 'ssl_conn_is_ssl' and 'ssl_var_lookup' where modules
       providing SSL can install their own value supplying functions.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1886840 13f79535-47bb-0310-9956-ffa450edef68