KahaDB doesn't clean up old files

Over time, we're seeing that kahadb doesn't clean up old journal files. As a result, we eventually run out of disk space, or rather, we hit our usage limits and our producers are slowed down by the producer flow control mechanism. Others have experienced this problem too (for example, see http://mail-archives.apache.org/mod_mbox/activemq-users/201002.mbox/%3C27502591.post@talk.nabble.com%3E)

For now, we're moving back to the old amqPersistenceStore.