WASHINGTON (Reuters) - President Barack Obama hailed Muammar Gaddafi's death on Thursday as a warning to authoritarian leaders across the Middle East that iron-fisted rule "inevitably comes to an end," and as vindication for his cautious strategy toward Libya. Obama joined U.S. politicians and ordinary Americans in welcoming the demise of Gaddafi, who was for decades regarded as a nemesis of American presidents, and also claimed some of the credit for the Libyan strongman's downfall. ... "This marks the end of a long and painful chapter for the people of Libya who now have the opportunity to determine their own...