ATM, when the old value and the new value are equivalent,
- no value change command (VCC) is sent to the client
- no server-side listeners are notified.
While this looked ok at first, it can actually happen that a
client attribute has already changed its value and the according change notification is
under way (sits in the client queue or comes later in the server command list).
In this case the VCC should be sent.
We cannot detect this situation, therefore we must always force the value change command.
However, since from the server perspective, the value did not change, we will not notify any listeners.
Shortcutting endless update circles (hysterese) can therefore be done on the client side only .