Looking at the pop charts now, it's hard to remember that 20 years ago Saturday, an album was released that, for a time, changed music.  That album was Nevermind by Nirvana.  By January, thanks to its hit single "Smells Like Teen Spirit," Nevermind replaced Michael Jackson's Dangerous at #1 on the Billboard chart, and the alternative rock movement of the '90s had officially begun.  Grunge and flannel replaced hairspray and spandex, and soon the charts were filled with bands like Pearl Jam, STP, Soundgarden, Smashing Pumpkins and countless others who would've previously been thou