It seemed like a sure-fire bet: short the debt of a highly leveraged newspaper company that’s losing money. And for a while, it worked as investors piled up almost $500 million of wagers by buying credit-default swaps on the publisher, McClatchy Co. That is until hedge fund Chatham Asset Management stacked the deck with a deal that’s threatening to make those swaps all but worthless. The McClatchy situation is the latest trade that’s drawing jeers from critics who say the $11 trillion CDS market has devolved into a haven for manipulation.