AIG Faces Federal Grand Jury Probe  NEW YORK (Reuters) - A federal grand jury is investigating  products American International Group Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AIG.N target=/stocks/quickinfo/fullquote"&gt;AIG.N&lt;/A&gt; sold that  companies might have used to massage earnings, the world's  largest insurer by market value said on Thursday.