WASHINGTON — News that Hillary Clinton’s home e-mail server contained top-secret messages brings renewed attention to the security of her mail system and to the laws and regulations that control classified information.The new disclosure, and the question of whether it exposes her to more serious legal problems, was certain to escalate political heat on the Democratic presidential candidate ahead of today’s Iowa caucuses, the first contest on the 2016 nominating calendar.FBI Director James Comey, whose …