@Override
  public OperationFuture<Boolean> append(String key, Object val) {
    return append(0, key, val, transcoder);
  }
Append to an existing value in the cache.

<p>
Note that the return will be false any time a mutation has not occurred.
</p>

@param key the key to whose value will be appended
@param val the value to append
@return a future indicating success, false if there was no change to the
        value
@throws IllegalStateException in the rare circumstance where queue is too
          full to accept any more requests
src/main/java/net/spy/memcached/MemcachedClient.java