APRIL 1971. It’s a cold night at the outdoor Greek Theatre and the seats are made of stone. But at the Berkeley Jazz Festival, the music is always worth the pain. Up on stage, a river of sound streams from Alice Coltrane’s harp, and Archie Shepp wails out on his tenor sax. With bassist Jimmy Garrison and drummer Clifford Jarvis driving the rhythm, the power of the music lifts up even those in the nosebleed seats.