It was an American dream that has failed to become a reality. For much of the last decade, enthusiasts from President George W. Bush down have touted corn-based ethanol as something approaching a superfuel, a home-grown alternative to foreign oil that would help cut smog and bring hope to struggling farmers. It has not worked out that way. Instead, the ethanol industry has undergone a great boom and bust in which a Financial Times analysis has found investors as savvy as Bill Gates, Microsoft’s founder, have collectively lost billions of dollars.