CONCORD - When the money’s on the line, NASCAR’s best drivers better keep their feet on the gas. With a $1 million payday, the NASCAR Sprint All-Star Race at Charlotte Motor Speedway already offers the richest per-mile winner’s purse in motorsports at more than $7,400 for each mile raced. But this year, the pot gets even sweeter with the introduction of Bruton’s Big Bonus. When NASCAR’s best take...