Northwest, Sabre Tussle Heats Up  CHICAGO (Reuters) - A dispute between Northwest Airlines  Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=NWAC.O target=/stocks/quickinfo/fullquote"&gt;NWAC.O&lt;/A&gt; and Sabre Holdings Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=TSG.N target=/stocks/quickinfo/fullquote"&gt;TSG.N&lt;/A&gt; intensified on  Wednesday as the airline sued Sabre for changing the way it  displays fares on its computerized reservation system.