Aidin Vaziri | After committing a tally of his medical conditions and personal insecurities to record earlier this year with Sun Kil Moon’s stark double-album set, “Benji,” you might think Mark Kozelek had nothing more to hide. But then there’s “Sings Christmas Carols,” in which he lends his dour voice and classical guitar mastery to a set of seasonal standards delivered with a straight face and borderline cheer. Who knew the lonely voice of the Red House Painters could get so worked up over a bit of tinsel and pine? From “Away in a Manger” to “God Rest Ye Merry, Gentlemen,” the San Francisco singer-songwriter works hard to capture just the right hymnal atmosphere on each song, sometimes at the risk of his own signature sound. His enthusiasm for the project really boils over on “Christmas Time Is Here,” where he capably inhabits the role of fellow depressive Charlie Brown.