VetiverWednesday, April 8, 2009Great American Music HallBetter than: There's a fine line these days between jam bands and folk-leaning rock bands with guitar riffs that linger like the scent of patchouli. Vetiver loosens the reins without awakening the Dead too much.There's a new lightness to Vetiver's material, a breezy happy-go-luckiness that adds a chipper pace and attitude to the local band's latest record, Tight Knit. So even as the group furthers its forays into soft rock, there's a kick