Add NewGRF feature: Extra station name strings

These are used when all the default names have been used up,
instead of "Town Station #NNN".

src/openttd.cpp

@@ -464,6 +464,7 @@ static void ShutdownGame()
 	_game_load_date_fract = 0;
 	_game_load_tick_skip_counter = 0;
 	_game_load_time = 0;
+	_extra_station_names_used = 0;
 	_loadgame_DBGL_data.clear();
 	_loadgame_DBGC_data.clear();
 }