mod_proxy_ajp: Forward SSL_PROTOCOL. Forthcoming

versions of Tomcat know how to extract the information
and provide it as a request attribute.

Compatibility is not broken, because we forward it
as a named request attribute, not with a new byte
encoded name.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1661067 13f79535-47bb-0310-9956-ffa450edef68