Puerto Vallarta (PVDN) - As American youth prepares to pack up their books and hit the beaches, many are hearing an increasingly strong warning from the U.S. Government: think twice before traveling to Mexico. Experts believe that some resorts, which have long been considered safe areas, may actually be controlled by Mexican drug cartels. “There is a cartel presence in these resorts,” said Robert Almonte, a former U.S. marshal in the western dist…