This reverts commit 8fc9f1e5ef.
As I already feared, this does not work right. The entire linking/unlinking code is simply too fragile. So no protection here against inept tinkering.
Some people apparently have to toy around with the engine's innards without fully understanding them. :(
When properly used the saveguards should never be triggered.
* refactored FBoundingBox so that the game dependent members are global functions now.
* changed some methods of the model renderer to take a render style parameter instead of a full actor.
