NEW YORK( Reuters)-A former Taliban commander previously accused of kidnapping an American journalist is expected to plead not guilty on Friday to murdering three U.S. troops in Afghanistan in 2008.U.S. prosecutors in Manhattan last week unsealed new charges against Haji Najibullah, who prosecutors say was a Taliban commander in Afghanistan's Wardak Province, which borders Kabul.... Taliban fighters under Najibullah's command attacked a U.S. military convoy, killing U.S. Army Sergeants First Cl