allow you to export var MODULES that will override what is in modules.conf for that build.  work a little harder to try to make it so you can do make in a module directory.  More on that later

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@4583 d0543943-73ff-0310-b7d9-9358b9ac24b2