Use two optional functions from mod_ssl so that we

can receive both is_ssl and ssl_var for ajp protocol.
This is combined work based on patch from Brad Boyer and
Joe Orton's suggestion to use ssl_var_lookup.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@160690 13f79535-47bb-0310-9956-ffa450edef68