 By Angelo Amante ROME Reuters - The arrest of Sicilian mafia boss Matteo Messina Denaro deals a powerful blow to the mythology of the Cosa Nostra, toppling a symbol of the groups resistance to police efforts to break up organised crime. Messina Denaro, 60, was Italys most wanted mafia boss and had been on the run for three decades. He had been sentenced in absentia to a life term for his role in the 1992 murders of anti-mafia prosecutors Giovanni Falcone and Paolo Borsellino. His arrest come... 