Stocks sold off Friday as the morning's brief optimism, fueled by a better-than-expected jobs report, simply ran out of gas. The Nasdaq tumbled 1.3%, the Dow Jones industrial average lost 1.1% and the S&P 500 fell 0.9%. Volume fell on both exchanges, according to preliminary data. The jobs report raised hopes that the economy was on the mend. But the opening's gains couldn't stick, and downside reversals cropped up among the major indexes, which