TORONTO - North American stock indexes extended last week's slump, as the Dow Jones industrial average plunged nearly 1,600 points during Monday's trading session ? bringing an end to a period of record-setting calm in the market. In New York, the Dow finished the day down 1,175.21 points to 24,345.75, or 4.6 per cent, erasing its gains for the year. The S&P 500 index fell 113.19 points to 2,648.94 and the Nasdaq composite index dropped 273.42 ...