Christopher Durang, a Montclair-born playwright, has died at 75

Christopher Durang, the Tony-winning Montclair-born playwright who died Tuesday, was a cultural advance scout.The frontiers he explored, in outrageous black comedies like “Sister Mary Ignatius Explains it All For You” (1979), “Beyond Therapy” (1981), and “Why Torture is Wrong, and the People Who Love Them” (2009), blazed a trail for others.”My kids watch ‘South Park,’…