Stocks were having another back and forth session Wednesday, and the Dow Jones Industrial Average dropped under 13,000 for the first time in four months, as continuing credit market jitters kept the market on edge. After recovering from an early swoon to rise by as many as 90 points, the Dow gave back all of those gains and more, and was recently down 130 points at 12,899. The index last closed below the 13,000 mark on April 24. Elsewhere, the S&P 500 was losing 13 points at 1413, and the Nasdaq Composite was sliding 26 points to 2473. The action...