linkingObjectsOfClass:forProperty: doesn't support subclasses

[timothycosta]

I'm indifferent to whether this is implemented or not, and I would imagine there are performance reasons not to. But it should be added to the documentation that linkingObjectsOfClass:forProperty: returns results only for the exact class name passed to it, and is not aware of subclasses.

[mrackwitz]

This is not implemented yet. That's a still open feature request, we have yet to tackle. See #1109.
But I'd agree that we could improve our documentation around this topic.

[mrackwitz]

I opened #3040 to keep track of that.