applied patch from Gaetan to avoid missing a message. For background see: http://www.nabble.com/Ajax-amq%3A-Lost-messages-in-MessageListenerServlet-if-more-than-maxMessages-waiting-tf3785745s2354.html#a10705883
activemq/trunk/activemq-web/src/main/java/org/apache/activemq/web/MessageListenerServlet.java