Add ap_find_module_short_name() to quickly get the module short name

(i.e. symbol name with trailing "_module" removed) from the module_index.
To be used for logging.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@965408 13f79535-47bb-0310-9956-ffa450edef68