- Add exception to enforce max # of leases = 6, should be plenty
- Rewrite TunnelPool.locked_buildNewLeaseSet() so it doesn't add lots of
leases and then immediately remove them again, triggering
the new leaseSet size exception
- Remove the now unused LeaseSet.removeLease(lease) and
LeaseSet.removeLease(index)
- Store first and last expiration for efficiency