By Paul Taylor PARIS (Reuters) - Grigoris Lemonis, a 73-year-old Athens pensioner, uses his 580 euro ($760) monthly state pension to support his wife and the family of his son, an unemployed cook with two small children and a wife who works occasionally as a cleaner. Three-generation families surviving on a single income are increasingly common across southern Europe as mass unemployment tears at the fabric of closely knit societies. ...