KMart to Buy Sears in \$11.5 Billion Deal  NEW YORK (Reuters) - Discount retailer Kmart Holding Corp.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=KMRT.O target=/stocks/quickinfo/fullquote"&gt;KMRT.O&lt;/A&gt; will buy department store operator Sears, Roebuck    Co. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=S.N target=/stocks/quickinfo/fullquote"&gt;S.N&lt;/A&gt; in a \$11.5 billion deal unveiled on Wednesday,  creating the third-largest U.S. retailer.