Update the ServerInfo listThreadDump to use the jdk 5 stack traces

The org.jboss.system.server.ServerInfo mbean's listThreadDump operation which display a tree of the system threads should be updated to use the jdk 5 mbeans which provides stack trace information when the bean that uses the java.lang.management.ThreadMXBean

http://java.sun.com/j2se/1.5.0/docs/api/java/lang/management/ThreadMXBean.html