Stocks strode ahead Thursday, but volume was only slightly higher. The Nasdaq chalked up a 0.9% gain while the S&P 500 and the Dow Jones industrial average added 1.3% and 1.5% respectively. The small-cap S&P 600 rose 1.8%. The IBD 50 gained 1.2%. Volume was slightly up on both major exchanges. The S&P 500 and the Dow retook their 50-day moving averages — positive moves, though the tests might not be over.