Add link to mod_setenvif docs. Add placeholder for mod_unique_id. Put

proxy & rewrite into alphabetic order. Note the modules which are not longer
part of Apache 1.3 (mod_browser, mod_auth_msql).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@79178 13f79535-47bb-0310-9956-ffa450edef68