"That's bluegrass music right there, y'all!" yelped Jamie Johnson of The Grascals, as fellow band member Kristin Scott Benson mesmerized the July 8 audience at Nashville's Ryman Auditorium with her blazing banjo. He was not kidding. For some 75 minutes, the two-time International Bluegrass Music Association's Entertainer of the Year winners plied their captivated crowd with music that al