Make APACHE_MODULE() accept an optional prerequisite module for configure.

Introduce the following configure time dependencies:
  mod_proxy_* (except proxy_html) require mod_proxy
  mod_dav_* require mod_dav
  mod_session_* require mod_session


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1234180 13f79535-47bb-0310-9956-ffa450edef68