Observable debugging and testing.  Doing some refactoring due to the fact that ObservableCollection.flatten()'s return value was not a true set--it did not enforce uniqueness.
Refactored ObservableSet.filterMapC to use similar code to ObservableList
Copied some code from ObservableSet.filterMapC into ObservableSet.enforceUnique because I think these will be very similar.  May be able to condense these into a single method somehow.  Build broken now.