RICHMOND, Va. (Reuters) - A U.S. federal judge on Thursday upheld a 2013 Virginia law requiring prospective voters to show an approved photo identification before they cast their ballots. The state's Democratic Party had challenged the law, signed by former Republican Governor Robert McDonnell, saying it was politically motivated and intended to deter young and minority voters from turning out on Election Day. "The court's mission is to judge not the wisdom of the Virginia voter ID law, but rather its constitutionality," wrote U.S. District Judge Henry Hudson in his decision. While he noted that the measure created an "inconvenience"...