* FTSEurofirst 300 up 0.8 pct, Euro STOXX 50 up 1.3 pct* EDF&aposs plunge takes 5.8 bln euros off its market value* Peugeot&aposs short-covering rally continuesBy Blaise RobinsonPARIS, June 19 (Reuters) - European stocks rallied on Thursday, with one blue-chip index near a six-year high, after the U.S. Federal Reserve signalled that over the long run interest rates would be lower than it had previ