Move the public mod_request.h header out of the include directory and back to modules/filters.

The current build of exports.c assumes that everything in include is part of the core, and so
putting the header there creates link errors.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@648254 13f79535-47bb-0310-9956-ffa450edef68