(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.

order_cmd.c

@@ -10,6 +10,7 @@
 #include "player.h"
 #include "news.h"
 #include "saveload.h"
+#include "vehicle_gui.h"
 
 enum {
 	/* Max orders: 64000 (64 * 1000) */