Stocks Fall, Wal-Mart, Oil, Dollar Weigh  NEW YORK (Reuters) - U.S. stocks fell on Tuesday as shares  of 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; extended their losses, oil  prices held near \$50 a barrel and the dollar hit a record low  against the euro.