https://issues.apache.org/jira/browse/AMQ-4248

Add expanded transmit callback interface so that a failure to transmit can be distinguished from normal operation and allow for no further attempts at dispatch fixing the current NPE when async dispatch is enabled. 

git-svn-id: https://svn.apache.org/repos/asf/activemq/trunk@1432487 13f79535-47bb-0310-9956-ffa450edef68