ROME (Reuters) - Billionaire showman Silvio Berlusconi has again astonished Italy with a storming comeback that has frayed nerves in European capitals and among investors, but the signs are his final gamble has failed. The 76-year-old media magnate and four-times prime minister looked down and out for much of 2012 after a jeering crowd hounded him from office in November 2011 as Italy tottered towards a Greek-style debt crisis. His indecision over whether to stand in this weekend's election brought his People of Freedom Party (PDL) to the brink of disintegration. ...