Blue Chips End Lower, Wal-Mart Weighs  NEW YORK (Reuters) - U.S. blue chips ended lower on Monday  after a disappointing sales forecast from the world's biggest  retailer, Wal-Mart Stores Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=WMT.N target=/stocks/quickinfo/fullquote"&gt;WMT.N&lt;/A&gt;, overshadowed a two-day  pullback in oil prices.