Add mod_example to the build system.

I also fixed a few bogosities in mod_example itself, mostly improved
ordering of the code; I also fixed the long-standing numbering mistake
for the order of the request processing stages, and added the hook
registering function to the module record.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85191 13f79535-47bb-0310-9956-ffa450edef68