(svn r2256) - Fix: Trains cannot find a depot when they are in a tunnel. (glx)

- Add: GetVehicleTrackdir() helper function.
- Codechange: Moved SortStruct from vehicle_gui.h to ttd.h, so the dependency from vehicle.h on vehicle_gui.h could be removed.
- Codechange: Typedeffed the VehicleTypes struct so it can be used as the type for Vehicle.type instead of "byte".
- Codechange: Removed prototype for VehicleSorter(), which had no implementation anymore and was never called.

vehicle_gui.c

@@ -73,7 +73,7 @@ void ResortVehicleLists(void)
 		}
 }
 
-void BuildVehicleList(vehiclelist_d *vl, int type, int owner, int station)
+void BuildVehicleList(vehiclelist_d *vl, VehicleType type, int owner, int station)
 {
 	int subtype = (type != VEH_Aircraft) ? TS_Front_Engine : 2;
 	int n = 0;