Royal Caribbean Cruise Line has offered a Boston cabbie and his wife seven all-expenses-paid days in the sun for returning $187,000 to a homeless man.Raymond MacCausland’s story of found-and-returned riches gained him national fame — but just a $100 reward.The lone Benjamin from the homeless man, whose own song of rags to inherited riches MacCausland helped set right, struck a chord with many, according to his wife, including the cruise company.