Fix compilation without boost log on g++ > 4.4
Fix compilation without boost log on g++ > 4.4

gale320/flexisip,BelledonneCommunications/flexisip,gale320/flexisip,biddyweb/flexisip,BelledonneCommunications/flexisip,gale320/flexisip,BelledonneCommunications/flexisip,biddyweb/flexisip,gale320/flexisip,BelledonneCommunications/flexisip,biddyweb/flexisip,biddyweb/flexisip