A global glut of oil will persist next year, putting further pressure on prices and raising the risk of unrest in some producing countries. That's the stark warning from the Paris-based International Energy Agency, which on Friday cut its forecast for global demand growth in 2015. It now sees demand growing by less than 1% next year. Oil prices have already fallen by more than 40% in six months, but there's little sign of that stimulating demand yet, or constraining production enough to remove excess supply. "Oil price drops are sometimes described as a 'tax cut' and a boon for...