MEXICO CITY — U.S. Ambassador Ken Salazar lashed out Wednesday at Mexico’s failure to accept aid in the fight against drug cartels, claiming the country “closed the doors” on security cooperation. In a press conference, Salazar launched his harshest criticism yet of rampant violence, police corruption and the Mexican government’s mistaken attitude that “there is no problem.” “When they just say ‘there is no problem, we have these statistics to show people there is no problem,’ that is not based