Routing the city's "scourge of illegal guns" will be the top priority in the next four years, Mayor Bloomberg pledged yesterday as he was sworn in for a second term. "Our most urgent challenge is ending the threat of guns and the violence they do," Bloomberg said during his inaugural address on the steps of City Hall — winning the loudest applause of the 19-minute speech. "Now we have a duty as well, one that rises above partisan politics, and one that we will pursue relentlessly: And that is to rid our streets of guns, and punish all of those...