Nick Vivarelli International CorrespondentThe battle is heating up between ex-Vivendi boss Vincent Bolloré and Mediaset founder and former Italian premier Silvio Berlusconi, European media barons and former friends.Four years after their botched pay-TV deal, where Vivendi walked away from plans to buy Mediaset’s pay-TV unit — a pact that was supposed to lead to a strategic alliance that could have given the family-controlled companies scale to compete against streamers — the barons and their