Rarities, B-Sides And OtherAmazon. com The Sarah McLachlan cottage industry rolls with Rarities. This disc of hard to finds and extended remixes offers some choice morsels for casual fans and a whole plateful for the faithful. The Freedom Sessions proved that McLachlan can do some nice stuff with a cover tune, and she offers a sweet handful here. Fellow Canadians Gordon Lightfoot and Joni Mitchell get lushed out respectively with "Song For A Winter's Night" and "Blue," and