@Override
      public void receivedStatus(OperationStatus s) {
        rv.set(s.isSuccess(), s);
      }
Delete the given key from the cache of the given CAS value applies.

@param key the key to delete
@param cas the CAS value to apply.
@return whether or not the operation was performed
@throws IllegalStateException in the rare circumstance where queue is too
          full to accept any more requests
src/main/java/net/spy/memcached/MemcachedClient.java