renamed fmt to f in Debugf (since it collided with the fmt package...). added a way to close the Server by closing the input channels of all sessions. if input session is closed then Handle function terminates, which closes the connection. since oldSubscriptions is no longer an array, we now have to iterate over it as an object. changed all null comparisons to follow frontend standards. check that heartbeater is not null before clearing it. added test TestReSubscribeOnServerDeath.