Juan Carlos I of Spain returned from exile Thursday to a mix of cheers and potential controversy.  Spain's ex-king, 84, who fled Spain under a financial cloud two years ago, arrived by private flight for a weekend visit at Vigo Airfield on Spain's northwest Galician coast.   The purpose and itinerary of his four-day return, only announced officially the day prior, and essentially motivated by the former king's desire to participate in a sailing regatta — onboard a ship called 'The Rascal' — have caused considerable waves and government embarrassment.   Dressed in a blue blazer and walking with a cane, Juan Carlos was met and embraced by his daughter, Princess Elena, at the airport (who c ...