@Override
  public OperationFuture<CASResponse>
  asyncCAS(String key, long casId, int exp, Object value) {
    return asyncCAS(key, casId, exp, value, transcoder);
  }
Asynchronous CAS operation using the default transcoder with expiration.

@param key the key
@param casId the CAS identifier (from a gets operation)
@param exp the expiration of this object
@param value the new value
@return a future that will indicate the status of the CAS
@throws IllegalStateException in the rare circumstance where queue is too
          full to accept any more requests
src/main/java/net/spy/memcached/MemcachedClient.java