Graphs Lab Changes (again)

I have made a few changes that shouldn't affect most people, but I'm letting you know about them anyway. (1) The compareTo code for WeightedEdge has been changed to actually take the weight into account. (2) The staff tests have been fixed to rely less on the graphs you guys make, and now use the staff graph to test your algorithms. (3) The staff code now takes self-loops into account; you will not be penalized if you do not. --Adam