When his Vietnam saga "Platoon" appeared, Oliver Stone felt it was a painful reminder of an aggressive mentality he hoped America had left behind. Two decades later, the country has fallen back on old habits, Stone said Sunday at the Cannes Film Festival, where "Platoon" had a 20th anniversary screening in advance of a new DVD edition coming May 30. A semi-autobiographical account of Stone's infantry experiences in Vietnam, "Platoon" depicts the combat with terrible savagery. With the current war in Iraq, the message has gone unheeded, said Stone, whose film won four Academy Awards, including best picture and director....