By Andrew MacAskill LONDON (Reuters) – Scotland will need checkpoints along its border with England for the first time in more than three centuries if it votes for independence and rejoins the European Union, according to a think tank report published on Thursday. The pro-independence Scottish National Party, which heads the Scottish government, wants to hold a second referendum on breaking away from the United Kingdom by the end of next year. Voters in Scotland, which has a population of around 5.5 million, rejected independence in 2014. But Scotland’s semi-autonomous government says Britain’…