Listen to this story Your browser does not support the <audio> element. CHINESE PANCAKES, pepper-beef stir-fry, fish with pickled mustard greens: to the average diner in China, these must sound like normal food orders. But to the staff at some restaurants they represent something else. These are code words that customers can use to signal that they would like a free meal. Such charitable schemes are becoming more common, as the Chinese economy sags. And restaurant owners report that an increasing number of people are using the code words. Huang…