Stocks turned modestly positive in early-afternoon action Wednesday, as a Fed announcement essentially matched expectations and cheered investors a little. The Nasdaq was up 0.2%, while the Dow Jones industrial average and the S&P 500 both gained 0.1%. Volume was tracking down from Tuesday's levels on both main exchanges. The Federal Open Market Committee announced at 12:30 p.m. ET that it will extend Operation Twist through the end of this year,