Description
Currently, when the Log4jServletFilter/Log4jServletContextListener are explictly configured in a web.xml, the application will fail to start on some Servlet 3.0+ container like Jetty 9.x.
For some type of projects, providing two different versions of war packages just to avoid this problem is not a viable option.
Maybe we better just warn the user instead of an throwing UnavailableException when the old method is used in Servlet 3.0 environment?