BERLIN/MADRID (Reuters) - On the eve of a crucial summit that could determine the future of the euro zone, German Chancellor Angela Merkel brushed aside increasingly shrill calls from Spain and Italy on Wednesday for emergency action to lower their soaring borrowing costs. European Union leaders go into the two-day meeting beginning on Thursday evening more openly divided than at any time since a still-widening debt crisis erupted in early 2010 after Greece revealed its deficit and debt were far higher than reported. ...