BOSTON (Reuters) - Mitt Romney's campaign accused President Barack Obama's re-election team on Friday of "unbelievable distortions," citing an online ad from a pro-Obama group in which a former steel worker seems to link Romney to the death of his wife. "I don't think a world champion limbo dancer could get any lower than the Obama campaign right now," said Eric Ferhnstrom, a senior adviser to Romney. The focus of his complaints was an ad released this week by Priorities USA, a pro-Obama "Super PAC," or political action committee. ...