Stocks Open Little Changed, Pfizer Falls   NEW YORK (Reuters) - U.S. stocks opened near unchanged on  Friday as oil prices hovered above \$44 a barrel while drug  company Pfizer Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=PFE.N target=/stocks/quickinfo/fullquote"&gt;PFE.N&lt;/A&gt; shares tumbled after it released an  research update.