Peace, love, war, sex and hair -- Sacramento will have a one-night opportunity to revel in hippie counterculture at Harlow's Thursday night. "HAIR: The American Tribal Love-Rock Musical" will rock the nightclub in the form of a concert. Local theater company Artistic Differences will perform musical numbers from "HAIR" as part of the company's Summer of Rock series, which kicked-off with "Tommy" at the Crest on Memorial Day. Many of the original cast members from the company's five-week run of the show in 2007 will return to sing the numbers, accompanied by a seven-piece band.   "HAIR" the musical brings to light a group of young flower children who band together as a "tribe" in the East