What does it take to direct a festival of contemporary music? A composer? How about conductor? Robert Spano, who is directing this summer’s Tanglewood Festival of Contemporary Music. “Mr. Spano has been an inspired choice. He assembled an eclectic program – eight concerts in five days – that touched on everything from the most abstruse essays in rhythmic and harmonic complication to works rooted in rock and jazz, and with classics like Elliott Carter’s String Quartet No. 1 (1951) and Karlheinz Stockhausen’s “Gesang der Jünglinge” (1956) nestled against freshly minted scores.”