TAKING CHARGEThe Dark Lordhttp://www.tpmmuckraker.com/archives/004449.php[Spencer Ackerman] A long, twilight struggle between Dick Cheney and the forces of evil is the subject of an impressive new Frontline documentary, "Cheney's Law," airing tomorrow on PBS. . . .It deftly ties the Ashcroft-hospital bed incident to the appointment of Attorney General Alberto Gonzales and the subsequent U.S.