(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.

aircraft_cmd.c

@@ -13,6 +13,7 @@
 #include "sound.h"
 #include "player.h"
 #include "airport.h"
+#include "vehicle_gui.h"
 
 static bool AirportMove(Vehicle *v, const AirportFTAClass *Airport);
 static bool AirportSetBlocks(Vehicle *v, AirportFTA *current_pos, const AirportFTAClass *Airport);