(previews start on July 7; opens on July 14) Nothing like rape, murder, and accusations of witchcraft to lend shivery chills to hot nights. The Potomac Theater Project launches a typically sable summer season. There's Howard Barker's biblical tale "Judith: A Parting from the Body," Caryl Churchill's 17th-century English story "Vinegar Tom," and a revival of Howard Barker's "Scenes from an Execution," a drama about a 15th-century Venetian painter, starring Jan Maxwell.