FRIDAY: >> Octogenarian fiddler Joe Thompson (at right), said to be the last black traditional string band player, plays a free show at The Kennedy Center’s The Millennium Stage with fellow folk musicians Wayne Martin on fiddle and Bob Carlin, a clawhammer style banjoist. 6 p.m. >> Space rockers The Gulf sold out their D.C. show in April, and are coming back to play at the Red and the Black with the Joonies, Twin Earth,…