By Stephen Culp NEW YORK (Reuters) – The S&P 500 advanced on Friday, rebounding from selloff to rally and then paring gains near the end of a tumultuous week marked by heightened volatility as investors weighed mixed corporate earnings, geopolitical turmoil and an increasingly aggressive Federal Reserve. The Nasdaq joined the S&P 500 in positive territory, with tech shares, led by Apple Inc, doing the heaviest lifting. But the Dow reversed its gains and was last slightly lower. The three indexes remain on track to close below last Friday’s levels, marking the S&P 500’s fourth straight weekly d…