026 Bounding box calculation: the bbox for the Barcelona.iv model is
    _very_ sub-optimal. (SGI Inventor seems to make a perfect fit.)

    Update, some further investigations made: the bug disappears if we
    remove the invalid face (there are two "-1" in a row in the
    coordIndex field). Bbox-calculation code should match the
    rendering code in what action to take when detecting this case, so
    bboxes matches the geometry that actually gets rendered.

    20020915 mortene.
