Stocks ended their four-day winning streak with a bang today, after a shooting in Ottawa spooked the markets. Getty Images The NYSE use to look like this. This is New York Mercantile Exchange. The S&P 500 finished down 0.9% at 1,927.11 today, while the Dow Jones Industrial Average dropped 153.49 points, or 0.9%, to 16,461.32 and the Nasdaq Composite fell 0.8% to 4,382.85. [...]