ObservableCursor aliases all lists it passes to callbacks

[Dominique Quatravaux]

There is only one _this._data array per ObservableCursor, that gets passed around by reference to all _observers every time _handleChange runs. As a result, downstream consumers that try to filter out null changes (such as Angular's | async pipe, which relies on WrappedValue) get confused, as they compare old and new values by keeping a reference to the old one.

#100 might be a symptom of the same cause.