The future or the flavor of the month? Some of the businesspeople who crowded around as driver David Cox pumped natural gas into his 18- wheeler Monday weren’t sure that the fuel – plentiful and cheap in the United States because of shale drilling – is inevitable as a substitute for diesel. But that didn’t stop them from pulling out their iPhones to document the moment as they considered the evidence. “You see the oil companies getting into it,” said Marion Barnes, president of Frontier Trailer Associates in Rocky Mount, N.C. “They’re spending billions, not millions. Boone Pickens is spending...