new methods that block the entry of an object. Implemented on machines to avoid receiving to signals at the same simulation time
minor corrections to queue. removeEntity of Queue now also signalReceiver
Machine now controls if its entry is assigned before returning True from canAccept
Jobshop machines also check if their entryIsAssigned before returning True from canAccept
managedJobQueues now sort not for receiver but for thecaller of their haveToDispose method