By Steve Holland FORT DIX, N.J. (Reuters) - President Barack Obama used a holiday season visit to a U.S. military base on Monday to issue a tough warning to Islamic State militants, saying a U.S.-led coalition will permit no safe haven to the group and will destroy it eventually. Obama spoke to hundreds of camouflage-wearing troops in a hangar at Fort Dix to thank the U.S. military for its actions around the world. In a display of bipartisan support for the troops, Obama was joined by New Jersey's Republican Governor Chris Christie, a potential candidate to succeed Obama in 2016. The U.S. ...