[LOG4J2-359] Changed the Servlet 3.0 auto-initializer so that it does nothing in a Servlet 2.5 or older application. This ensures behavioral consistency across containers. Thanks to Abhinav Shah for the patch this change was based on.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1519193 13f79535-47bb-0310-9956-ffa450edef68