Cloud Nine **** Barbecue **** The Christians ****
                  By: David ShewardConstance Shulman, Arden Myrin: "Barbecue"Theatrical conventions are shattered in three Off-Broadway productions as playwrights explore the hot button topics of race, gender, and religion. Two are contemporary (Robert O'Hara's Barbecue and Lucas Hnath's The Christians) and one is over three decades old (Caryl Churchill's Cloud N…