By Bruce Horovitz, USA TODAY McDonald's fries have always given Burger King heartburn - but watch out Ronald McDonald. In a move destined to shake up the fast-food industry, Burger King Tuesday will unveil a simple but startling french fry innovation: french fries with 30% less fat and 20% fewer calories than BK's current fries. (And 40% less fat and 30% fewer calories than McDonald's fries.)...