Marshal Cohen, chief industry analyst at NPD Group Inc., talks about U.S. consumer spending and the outlook for the back-to-school shopping season and luxury retailers.   Sales at U.S. retailers, led by Target Corp. and Limited Brands Inc., surpassed analysts’ estimates last month as discounts and lower gas prices in the U.S. enticed consumers to spend. Cohen speaks with Mark Crumpton on Bloomberg Television’s "Bottom Line."