On the night before Sub Pop co-founder Bruce Pavitt released an e-book chronicling Nirvana’s first European tour (including never-released photos), fellow Seattle grunge golden era rockers Soundgarden took to Letterman for a live performance. Their new album King Animal, their sixth studio full length by my count, is out now. They played King Animal track “Been Away Too Long” for Dave L and crew. Crazy to see them still rockin…