Avici Sees Revenue Shortfall, Shares Drop  CHICAGO (Reuters) - Avici Systems Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AVCI.O target=/stocks/quickinfo/fullquote"&gt;AVCI.O&lt;/A&gt;, which  makes equipment that directs traffic over the Internet, on  Monday slashed its revenue outlook for the current quarter  because customers have delayed network expansions, and its  shares lost nearly a third of their value.