(NORTH ADAMS, Mass.) – Bluegrass legend Del McCoury and progressive bluegrass/jam-band Yonder Mountain String Band headline FreshGrass: A Festival of Bluegrass + Art, MASS MoCA’s first-ever bluegrass festival, on Saturday, September 24, 2011, from 6 to 11 p.m. and Sunday, September 25 from 11 to 6 in MASS MoCA’s Hunter Center and Courtyard C. FreshGrass…