MEXICO CITY (Reuters) – U.S. anti-narcotics agents have discovered a drug-smugglers’ tunnel running under the U.S.-Mexico border and equipped with a rail track, electricity and ventilation system, the U.S. Department of Justice said. The so-called “narco-tunnel” led from the Mexican city of Tijuana to a warehouse 300 feet from the border in San Diego, California, the department said in a statement. U.S. authorities arrested six people for their alleged involvement in the drug-running scheme. They are accused of conspiring to distribute cocaine, heroin and methamphetamine, among other crimes. “…