New York Times: It was supposed to help clean the air, reduce dependence on foreign oil and bolster agriculture. But a little known market in ethanol credits has also become a hot new game on Wall Street. The federal government created the market in special credits tied to ethanol eight years ago when it required refiners to mix ethanol into gasoline or buy credits from companies that do so. The idea was to push refiners to use the cleaner, renewable fuel, or force them to buy the credits. A few worried that Wall...