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

If 0 is passed in as the CAS identifier, it will override the value
on the server without performing the CAS check.

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

@param <T>
@param key the key to whose value will be appended
@param val the value to append
@param tc the transcoder to serialize and unserialize the value
@return a future indicating success
@throws IllegalStateException in the rare circumstance where queue is too
          full to accept any more requests
src/main/java/net/spy/memcached/MemcachedClient.java