Aimee Mann never seemed like one of pop’s 500 likeliest candidates to release a Christmas album, but last year’s One More Drifter in the Snow was a tasteful, minor-key treat, and her “1st Annual Christmas Show” at the Birchmere last December was one of the best concerts of 2006. As she promised she would at the end of last year’s freewheeling interfaith revue, she’s hitched up the sleigh again this year for a monthlong yule-tour…