MEXICO CITY — Mexican democracy has come a long way from the days when the ruling party would give out washing machines for votes and rip up ballots with the wrong box checked off. Today, electoral regulators preside over an elaborate system of safeguards that have made stealing the presidency at the ballot box impossible, political analysts say. But they warn that the country’s July 1 election remains vulnerable to subtler forms of tampering and the shadowy influences of organized crime, along with some new twists on the old dirty tricks.