Removed dead code that nothing uses.
Added a new type of priority: a super-priority.  An event with this
priority can preempt any event running with a standard or boosted
priority.  This priority should be used sparingly.
Upated boosted manager to support super priorities.  Importantly, do not put them in boostedmanager's event_list.  This is because event_list is supposed to keep track of only events that are/can become boosted.
Now emitting two versions of external facing methods: one passes in an
additional ralph.EventPriority.IsSuperFlag.  Using this signature, a
programmer can start a potentially super transaction.  Using the other
signature, will always create standard/boosted transactions.
Added test to ensure that super events can preempt boosted and other
events.