YOU MIGHT THINK THAT ENERGY STOCKS HAVE HIT their highs, but Chuck Clough considers that a delusion. The chief of Boston-based Clough Capital Partners says that while crude prices have backed off, natural-gas supplies are getting tighter, as North American gas fields are being depleted. "There will be a second level of tightening," Clough predicts confidently. "This is still in the early stages of being recognized by the capital markets. I hate to use this metaphor, but we're in the third inning."