Lexington, Ky. — Ten years ago, the future of America’s oldest chain restaurant franchise was in question. A&W, owned by YUM! Brands, was struggling. But then a group of franchise owners formed a partnership and bought the company, which was 92 years old at the time, on Dec. 19, 2011. A&W is still the only major restaurant brand 100% owned by its franchisees. Since the acquisition: Same-store sales have increased every year, reversing 7 years of declines; sales this year are up 10.2%, following last year’s 9.2% growth. Average unit …