Global Crossing Stock Down 25 Percent  NEW YORK (Reuters) - Shares of Global Crossing Ltd.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=GLBCE.O target=/stocks/quickinfo/fullquote"&gt;GLBCE.O&lt;/A&gt; fell as much as 25 percent on Monday on concerns it  could face a second bankruptcy after it said it is cutting 600  jobs as it negotiates with lenders for much-needed financing.