@:allow should not be inherited

I just hit into the following.

In heaps I have some class `h2d.Tile` with `@:allow(h2d)` so the classes in `h2d` package can access its private for implementation reason.

If I extend a `h2d` class into my own project custom class (which is not part of the `h2d` package) then I can still access the `h2d.Tile` privates.

I don't know if it was there from the start or if it's a regression but I think it should be fixed.