code: @Override
    public <T> OperationFuture<Boolean> prepend(long cas, String key, T val,
        Transcoder<T> tc) {
      return asyncCat(ConcatenationType.prepend, cas, key, val, tc);
    }
docs: Prepend 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 cas cas identifier (ignored in the ascii protocol)
  @param key the key to whose value will be prepended
  @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