Safer level crossings: add setting to improve RV level crossing safety.

src/vehicle_func.h

@@ -165,6 +165,7 @@ static inline uint32 GetCmdSendToDepot(const BaseVehicle *v)
 }
 
 CommandCost EnsureNoVehicleOnGround(TileIndex tile);
+CommandCost EnsureNoRoadVehicleOnGround(TileIndex tile);
 CommandCost EnsureNoTrainOnTrackBits(TileIndex tile, TrackBits track_bits);
 
 extern VehicleID _new_vehicle_id;