Complete cleanup of global variable use by mod_example. This should take away

any existing reservation about thread-safety of this code.  Add warning that 
this code is now too top heavy and implements too many obscure callbacks to 
serve a s point of departure for one's own development effort. 



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@550636 13f79535-47bb-0310-9956-ffa450edef68