a way to sort objects in the priority queue on a secondary(etc) attribute when the primary attribute is equal

[antonytrupe]

This will probably require a function in each object that takes a parameter that is a second object.
This also means evaluate in PriorityQueue will need to be modified to pass the second object to the first object.
This is the same as overriding compareTo in java.

[antonytrupe]

re: issue #33