The owners of a small South End gallery say they had the best of intentions when they commissioned a famous and often mischievous street artist to install a massive political mural on a construction wall lining one of the artiest strips of the South End. The mural, 13 feet high and nearly a block long, features multiple composite portraits of Democratic presidential candidate Barack Obama and Abraham Lincoln, their faces melded together in a rainbow of colors. It is meant, the gallery said, to inspire dialogue. That it did. The morning after artist Ron English and his band of...