WASHINGTON (Reuters) – A lawyer for former media baron Conrad Black urged the U.S. Supreme Court on Tuesday to overturn his fraud conviction, and several justices asked whether the federal law at issue was too vague. The Canadian-born Black, a member of Britain's House of Lords, has been in prison since March 2008, when he began serving a 6 1/2-year sentence for fraud and obstruction of justice. Attorney Miguel Estrada, representing Black and two ex-colleagues who were found guilty of defrauding shareholders of one-time newspaper publishing giant Hollinger International Inc, argued before the Supreme Court that all convictions in the...