Snow drifts reaching up to rooftops kept tens of thousands of villagers prisoners in their own homes Saturday as the death toll from Europe's big freeze rose past 550. More heavy snow fell on the Balkans and in Italy, while the Danube river, already closed to shipping for hundreds of kilometres (miles) because of thick ice, froze over in Bulgaria for the first time in 27 years. Montenegro's capital of Podgorica was brought to a standstill by snow 50 centimetres (20 inches) deep, a 50-year record, closing the city's airport and halting rail services to Serbia because of an avalanche....