Models for the race detector

[akashlal]

The race detector cannot find racing accesses to a collection (like List, Dictionary, etc.) because we do not instrument mscorlib. We should have means of adding this knowledge, e.g., List.Add will race with List.Remove but List.Item[i].get() doesn't race with List.Item[j].get().

@t-rasmud I've created this issue so we don't forget.