FDA KOs Allergan Psoriasis Treatment  NEW YORK (Reuters) - U.S. regulators won't approve Allergan  Inc.'s &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AGN.N target=/stocks/quickinfo/fullquote"&gt;AGN.N&lt;/A&gt; experimental treatment for the skin disorder  psoriasis based on the data submitted, the company said on  Monday.