1991 was a watershed for popular music—the year when the gains of punk and post-punk stormed the gates of the mainstream. Over the past few years, Patti Smith, the godmother of punk, has returned to this seminal period by recording cover songs from two landmark ‘91 albums. From Nirvana’s Nevermind (September ‘91)there’s a transporting remake of “Smells Like Teen Spirit,” and, now, from U2’s Achtung Baby (November ‘91), her interpretation of “Until the End of the World.”