resolve https://issues.apache.org/activemq/browse/AMQ-2584 for AMQ store, if a write was outstanding when a second add arrives, the addition was ignored but the additonal file reference was not ignored leading to a dangling ref to a data file that prevented it being reclaimed
activemq/trunk/activemq-core/src/main/java/org/apache/activemq/store/amq/AMQMessageStore.java