Costco Posts Higher First-Quarter Profit  NEW YORK (Reuters) - Costco Wholesale Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=COST.O target=/stocks/quickinfo/fullquote"&gt;COST.O&lt;/A&gt;, the  largest U.S. warehouse club, posted a 21 percent increase in  quarterly profit on Thursday.