Their father was a hero. Today, at his funeral, his 6-year-old twin sons reported for duty. Officer Mark Davis was, to his 6-year-old twins, a real-life superhero. He was "Daddy Cop." They loved his shiny badge, his "cool" car, and the way he looked in his uniform. When he was killed in the line of duty, their world shattered. The morning of the funeral, his wife, Jessica, laid out two small black suits. But the boys, Ben and Leo, shook their heads and refused. "No, Mommy," Ben whispered, his vo