possible change to Memcache api

cas.scala

  def cas(key: String, flags: Int, expiry: Time, value: Buf, casUnique: Buf): Future[JBoolean] = {
    cas2(key, flags, expiry, value, casUnique).flatMap {
      case Some(b) if b => JavaTrue
      case Some(b)      => JavaFalse
      case None         => JavaFalse
    }
  }

  private[this] val SomeJTrue: Future[Option[JBoolean]] = Future.value(Some(true))
  private[this] val SomeJFalse: Future[Option[JBoolean]] = Future.value(Some(false))

  def cas2(key: String, flags: Int, expiry: Time, value: Buf, casUnique: Buf): Future[Option[JBoolean]] = {
    try {
      service(Cas(key, flags, expiry, value, casUnique)).flatMap {
        case Stored()   => SomeJTrue
        case Exists()   => SomeJFalse
        case NotFound() => Future.None
        case Error(e)   => Future.exception(e)
        case _          => Future.exception(new IllegalStateException)
      }
    } catch {
      case t: IllegalArgumentException => Future.exception(new ClientError(t.getMessage))
    }
  }