Chan Marshall, 31, the singer, songwriter, guitarist, pianist and pretty much sole member of Cat Power, may be the most effective anti-performer around. Her quiet, plain-Jane alto is always fading to a whisper, her instrumental skills are beginner-level functional, her song structures are simple, her tempos dirgelike. She won a cult following in the mid-’90s with her postpunk debut album, “Dear Sir,” released on Sonic Youth drummer Steve Shelley’s label; a less small cult following with the minimalist 1998 “Moonpix” and the equally spare and moody “The Covers” in 2000–with well-chosen songs by Dylan, the Stones and the regrettably obscure Michael Hurley....