(svn r16527) -Codechange: use static member functions instead of simple casts when converting Vehicle to specialised vehicle types. Includes safety check

src/vehicle_type.h

@@ -28,6 +28,8 @@ struct Train;
 struct RoadVehicle;
 struct Ship;
 struct Aircraft;
+struct EffectVehicle;
+struct DisasterVehicle;
 
 struct BaseVehicle
 {