Canceling rule, ref distances, cycled priorities.

-> When determining whether cancelation should start, I no longer take into account
    whether the priority is greater than zero when there's no information about the first priority.
-> Added reference distances to get the prioritary task,
    depending on who was the closest-to-leaf-node winner (current or reference).
-> Commented out the cycled priorities rule, as they CAN be cycled if they're not transitive.