Add reverse at waypoint orders.

The train will reverse when its tail is within the waypoint tile.
This is useful for reversing on train en-route, without creating
dedicated reversing sidings or platforms.

src/vehicle.cpp

@@ -1362,6 +1362,7 @@ void VehicleEnterDepot(Vehicle *v)
 			t->force_proceed = TFP_NONE;
 			ClrBit(t->flags, VRF_TOGGLE_REVERSE);
 			t->ConsistChanged(CCF_ARRANGE);
+			t->reverse_distance = 0;
 			break;
 		}