LONDON/FRANKFURT (Reuters) - Watson Pharmaceuticals Inc is close to buying Swiss-based Actavis for around $7 billion, marking the latest deal between generics companies racing to achieve economies of scale, three sources familiar with the matter said. The deal would see U.S.-based Watson, already among the world's five largest generic drugmakers, paying between 5.0 billion and 5.5 billion euros ($6.6-7.3 billion) for Actavis, a business of comparable size to its own, the sources said. ...