Stocks finished flat in a choppy session Monday, despite a round of merger activity and mostly good news overseas. After suffering their biggest weekly losses since June last week, the NYSE and S&P 500 each ticked up a fraction. Reflecting the market's pausing action, both had an inside day: The day's trading range was engulfed within the prior session's range. The Nasdaq slipped a fraction after being up as much as 0.5%. Volume tumbled on both