Priority queue scheduler
This is three contributions.
- Complete the set of comparison operators (< == != >) for Event and EventKey
- Alexander Krotov's PriorityQueueScheduler, from Bug 2503
- GCI 2019 patch which implements Remove for the PriorityQueueScheduler (the underlying std::priority_queue<> doesn't support remove() natively.)
Please DO NOT SQUASH these on merge.
Edited by Peter Barnes