VERTEX CONTROL

  void VertexControlClass::SetLimits(ObjectClass* object, int x, int y, int w, int h)
    Used for setting the position of a new vertex through AddObject() or the editing of
    an existing one (see visuallist.cpp).
    RetainZ is a property of ObjectControlClass and is used in VisuList.cpp for object
    resize and relocation.
    If RetainZ == true then the existing position is used to determine the current value
    in the z plane and this is used instead of Current_Visual->Depth to determine the
    3d component.  For Vertex, w and h are discarded.
