A listener that does the job of finding .tld files that contain
(other) listeners that need to be called by the servlet container.
This implementation is necessitated by the fact that it is only
after all the Configuration classes have run that we will
parse web.xml/fragments etc and thus find tlds mentioned therein.
Note: TagLibConfiguration is not used in jetty-8 as jasper (JSP engine)
uses the new TldScanner class - a ServletContainerInitializer from
Servlet Spec 3 - to find all listeners in taglibs and register them
with the servlet container.