Stocks Down on Coke Warning  NEW YORK (Reuters) - U.S. stocks were lower on Wednesday  after a profit warning from Coca-Cola Co. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=KO.N target=/stocks/quickinfo/fullquote"&gt;KO.N&lt;/A&gt; renewed  investors' doubts about earnings growth in the second half of  the year.