By Mari Saito, Fedja Grulovic and Pawel Florkiewicz KRAKOW, Poland/ISACCEA, Romania (Reuters) -People fleeing what had been the relative safety of western Ukraine joined thousands crossing into eastern Europe on Monday after Russia attacked a Ukrainian base near the border with NATO-member Poland. Ukraine said 35 people were killed at the base on Sunday. Moscow said up to 180 “foreign mercenaries” died and a large number of foreign weapons were destroyed. Ukraine also reported renewed air strikes on an airport in the west of the country. The number of refugees fleeing Ukraine since Russia inva…