Stocks mostly held gains at halftime Tuesday after erasing their early losses. The S&P 500 and Dow Jones industrial average tacked on 0.4%, while the Nasdaq was roughly flat. Volume was tracking up from Monday's levels across the board. Michael Kors (KORS) was little changed in big turnover, after being up up as much as 5% out of the gate. The Hong Kong-based clothing and accessories maker said fiscal second-quarter EPS increased 96% to 49 cents a