Vice President Joe Biden was in midtown today for a taping of the John Stewart show, and his security detail hit a bit of a snag while paving his way to the show. Three advance vehicles belonging to the NYPD were moving down 49th Street near 10th Avenue when they slammed into the back of a livery cab, officials said. The cars apparently had lights and sirens on at the time, officials said. Four people -- two NYPD officers and two civilians -- were injured, NYPD spokeswoman Barbara Chen said. Mr. Biden wasn't in the trail of cars at the...