Frederic Bouvier:

Frederic Bouvier:

 add an optional parameter that would be called to
 build the aircraft panel, so that flightgear's
 model_panel no longer duplicate code.

 add a pretrav callback to models so that we can
 filter out models when calling ssgCullAndDraw on
 the global scene.
 sgSetModelFilter( true ) means that we want to draw
 the models. Use false to cull them out.