(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.

misc.c

@@ -12,6 +12,7 @@
 #include "network_data.h"
 #include "network_server.h"
 #include "engine.h"
+#include "vehicle_gui.h"
 
 extern void StartupEconomy(void);
 extern void InitNewsItemStructs(void);