Reservations: fix time-tracking of table-driven reservations

Keep track of the current slot and major cycle explicitly to avoid
ambiguity when the budget charging is delayed into the next major
cycle due to a late interrupt or other sources of delay.
Reservations: request scheduler update for new active reservations

Don't forget to ask for a scheduler update when a reservation is
replenished but enters state ACTIVE_IDLE and there's nothing else
going on that triggers the scheduler by chance.
P-RES: improved handling of tardy jobs

Don't set a release timer for jobs that are tardy and already
released.