Stocks Mixed on Greenspan's Assessment NEW YORK - Investors were unmoved by Federal Reserve Chairman Alan Greenspan's improved assessment of the economy, and stocks remained mixed Wednesday in light trading.    While Greenspan said the economy has "regained some traction" after the summer's slowdown, he echoed Wall Street's concerns over energy prices, which have fallen from record highs in recent weeks but stubbornly remain above \$40 per barrel...