MILAN (Reuters) - Italian Prime Minister Mario Monti weighed in on the scandal surrounding Banca Monte dei Paschi di Siena on Thursday, rejecting suggestions that the authorities had failed to spot large trading losses threatening the bank. Already in need of a 3.9 billion euro bailout, Monte dei Paschi this week revealed loss-making derivatives trades that could cost it as much as 720 million euros (US$956 million), lurching center stage in a crucial general election campaign. ...