Stocks took a wallop Friday, and bigger volume added weight to the punch. The NYSE composite careened 3.1% and the S&P 500 2.8%. The Nasdaq and the Dow slid 2.5% each. Volume lagged for much of the session, and then kicked in. Trade was down as much as 20% to 30% at midmorning, but accelerated to finish up more than 10%. Friday was the end of the fiscal year for some mutual funds, which could account for the spike in volume. All the major indexes