added simple test to confirm decay works

The epsilon for the half-life decayed comparison might need to be adjusted when we actually get decay to return non-empty CompMaps.  This test should pass for v1.2 - it currently fails - even with @scopatz's `br` branch update.
This test will always fail because Cs-127 is not a daughter of Cs-137.  You probably meant for this to be Cs-137.