BERLIN (Reuters) - Chancellor Angela Merkel rebuffed pressure on Thursday for Germany, Europe's most powerful economy, to underwrite debt or guarantee bank deposits in the euro zone as Spain's soaring borrowing costs raised new alarm. Spain's 10-year bond yield hit a euro lifetime high of 7 percent - a staging post above which Greece, Ireland and Portugal were driven to seek international rescues - despite last weekend's euro zone agreement to lend Madrid up to 100 billion euros ($125 billion) to recapitalize ailing banks. ...