Finally have GiraphGraphComputer SideEffects working according to GraphComputerTest suite. Learned a bunch about aggregators in Giraph. Removed SideEffects.setIfAbsent() as it makes no sense in a BSP environment. For setup() you know if its absent or not. For execute() its a race to set -- so just use set. For terminate() you know if its absent or not with a get(). Just makes heads hurt. Fixed #44