RingBufferTruck does not release its payload

Run a write-heavy workload (PerfEval sequentialWrite) out of a trunk sandbox and watch as HBase eventually dies with an OOM: heap space. Examining the heap dump shows an extremely large retained size of KeyValue and RingBufferTrunk instances. By my eye, the default value of hbase.regionserver.wal.disruptor.event.count is too large for such a small default heap size, or the RBT instances need to release their payloads after consumers retrieve them.