Set the graphnodes of a function to active on entry

All graphnodes in a function must be set to active and dirty when entering or re-entering a function call.
PTAL @ke-yu @lukechurch 
If you use Linq, you could save two checkings: ``gnode.updateNodeRefList.Count == 0`` and ``gnode.updateNodeRefList.Count != executingNode.updateNodeRefList.Count``. :-) But it is minor. Never mind.