The CacheManagerContextListenerImpl class is
funtionally the same as CacheManagerImpl class but
implements an additional interface ServletContextListener
so that it will be automatically initiated and initialized
when the servlet container starts up, and will be destroyed when
the lifecycle of servlet container ends.
The PAERequestWrapper is for wrapper the original
HttpServletRequest before passing it to the RequestDispatcher.include().
A wrapper is needed because the PortletContainer and the
PortletApplicationEngine communicate with each other by setting the
PortletContainerRequest and PortletContainerResponse
to the request atributes.