Department of Homeland Security officials said Friday that they are improving the student visa system after a friend of Boston Marathon bombing suspect Dzhokhar Tsarnaev re-entered the country with an invalid visa. The officials said the department was “reforming the student visa system” to make sure customs and border officers get almost instant updates on visa information. Azamat Tazhayakov, a Kazakh student and friend of Tsarnaev, re-entered the United States in January with a visa that was no longer valid because he had stopped attending classes at the University of Massachusetts-Dartmouth. That information was apparently not relayed to customs officers....