ATLANTA -- Michael Stanley Dukakis, a self-described "very, very long- shot" candidate just 16 months ago, last night became the Democratic nominee for president and his party's best hope to win the White House since 1976. Earlier, Sen. John F. Kerry took to the convention hall podium, telling the delegates that the "moral darkness" of President Reagan's presidency will soon end. "A Republican president once reminded us, 'There is absolutely nothing to be said for a government of powerful men with the ideals of pawnbrokers,' " Kerry said. "That president's name was Theodore Roosevelt. And today Theodore Roosevelt would be...