LONDON (Reuters) - European shares edged up and the euro was flat on Wednesday as worries over contagion from Spain's banking sector were heightened by a sharp rise in the country's borrowing costs. Riskier assets have fluctuated all week as optimism and disappointment have alternately gripped financial markets, reflecting a high level of unease over whether Spain's banking crisis can be contained and if Greece will remain in the euro zone after its June 17 election. ...