Just what Fox needs: more news about American Idol's ratings free fall.  More viewers in the advertiser-coveted 18-to-49-year-old demographic watched the season finale' of the A & E cable show Duck Dynasty, than American Idol on Wednesday night.  The cable show outscored American Idol by 34 percent in that popular demo.  When it comes to the total number of viewers, Idol did come out on top with 12.5 million, as compared to Duck Dynasty with 9.6 million viewers.