I just got time to get the LadderSchedule working. I should probably do a
little optimization, but I am curious what is a good simulation that is
already in MASON to test it on? I know that it won't do well at all on
simulations that schedule every agent to step on every discrete time step,
but other simulations with erratic scheduling should do well.

The ordering is factored into the queue now as well. Whenever anything is
put into the bottom, it uses the comparator specified by the keys. This is
the only time the ordering comes into play. Otherwise the timestamp is
sufficient.