attempted fix for #137 so that we only requery the JMX tree again when our mbean is notified that there are new mbeans available (or mbeans have been unregistered) (thanks @rhuss!) also now we should always be using maxDepth=2 since we don't do a jolokia.register on the list operation; we just do 1 shot lists whenever we know the JmxTreeWatcher's counter has changed