By Anthony Boadle BRASILIA (Reuters) - Brazil's increasingly powerful evangelical Christians are tantalizingly close to electing one of their own as president next month in what would be a historic shift for the world's largest Catholic nation. Marina Silva, an environmentalist running neck and neck in polls with incumbent President Dilma Rousseff, is a Pentecostal Christian who often invokes God on the campaign trail and has said she sometimes consults the Bible for inspiration when making important political decisions. ...