Add a cut down, simple to debug, multicast tester than can be used to determine if multicast cluster membership is going to work in a given environment.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1487991 13f79535-47bb-0310-9956-ffa450edef68
Finally figured out how t get multicast working locally on my mac. Document it.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1487993 13f79535-47bb-0310-9956-ffa450edef68