By Paul Carrel FRANKFURT, Feb 28 (Reuters) - A dramatic anti-austerity vote leaves Italy lying outside the fortress the European Central Bank constructed around the euro zone last year and vulnerable to a market attack. This week's election leaves slim prospects for a durable, reform-minded government in Rome and exposes a flaw in the bond-buying defence plan the ECB put together last September - a weakness that could see the euro zone crisis roar back to life.