(svn r4466) -Fix: (FS#71) Game no longer crashes when the last vehicle serving a station has been deleted.

-Negative side effect: upon loading old games, stations whose last vehicle was a station have (temporarily) lower ratings.
   -Positive side effect: station.h no longer includes vehicle.h (breaks the station.h->vehicle.h->rail.h chain)

station.h

@@ -7,7 +7,6 @@
 #include "pool.h"
 #include "sprite.h"
 #include "tile.h"
-#include "vehicle.h"
 #include "newgrf_station.h"
 
 typedef struct GoodsEntry {
@@ -72,7 +71,7 @@ struct Station {
 	uint32 airport_flags;
 	StationID index;
 
-	VehicleID last_vehicle;
+	byte last_vehicle_type;
 	GoodsEntry goods[NUM_CARGO];
 
 	/* Stuff that is no longer used, but needed for conversion */