@Override
  public DummyListenableFuture<T> removeListener(
    GenericCompletionListener listener) {
    super.removeFromListeners(listener);
    return this;
  }
A very basic {@link ListenableFuture} to verify and test basic
add, remove and notification behavior.
src/test/java/net/spy/memcached/internal/DummyListenableFuture.java