Add road tile cached one way state, one way road section detection

src/saveload/extended_ver_sl.h

@@ -91,6 +91,7 @@ enum SlXvFeatureIndex {
 	XSLFI_MORE_VEHICLE_ORDERS,                    ///< More vehicle orders - VehicleOrderID is 16 bits instead of 8
 	XSLFI_ORDER_FLAGS_EXTRA,                      ///< Order flags field extra size
 	XSLFI_ONE_WAY_DT_ROAD_STOP,                   ///< One-way drive-through road stops
+	XSLFI_ONE_WAY_ROAD_STATE,                     ///< One-way road state cache
 
 	XSLFI_RIFF_HEADER_60_BIT,                     ///< Size field in RIFF chunk header is 60 bit
 	XSLFI_HEIGHT_8_BIT,                           ///< Map tile height is 8 bit instead of 4 bit, but savegame version may be before this became true in trunk