A competitor's Q2 report just caused investors to reassess Comcast stock.Comcast (CMCSA -4.82%) stock sold off in Friday's trading despite gains for the broader market. The company's share price closed out the session down 4.8% and had been off as much as 6.1% early in the session. The S&P 500 (^GSPC 0.40%) ended the day up 0.4%, and the Nasdaq Composite (^IXIC 0.24%) was up 0.2%. Charter Communications published its second-quarter report before the market opened this morning, and the report prompted a dram ...