Stevens Returns to U.K. After Detention LONDON - Puzzled and angry at being barred from the United States, Yusuf Islam, the singer formerly known as Cat Stevens, returned to London on Thursday vowing to find out why.    Surrounded by a throng of reporters at Heathrow Airport, Islam said it was ludicrous that he's on Washington's no-fly list, suspected of ties to terrorists, and said he would challenge the decision to block him from entering the country...