MEXICO CITY - The Mexican government, angered by a U.S. proposal to extend a wall along the border to keep out migrants, has struck back with radio ads urging Mexican workers to denounce rights violations in the United States. Facing a growing tide of anti-immigrant sentiment north of the border, the Mexican government is also hiring an American public relations firm to improve its image. Mexican President Vicente Fox denounced the U.S. measures, passed by the House of Representatives on Friday, as "shameful" and his foreign secretary, Luis Ernesto Derbez, said Monday the wall was "stupid." ADVERTISEMENT It's hard to...