Agence France-Presse: Riot officers fired pepper spray and non-lethal rounds Thursday to repel stone-throwing anarchist youths marching on a summit of the world’s most powerful leaders. Riot officers intervened after a 1,000-strong crowd, led by black-clad hardliners wearing goggles, helmets and masks and brandishing anti-capitalist banners, began to trek across Pittsburgh towards the G20 conference venue. The Group of 20 is a forum for the world’s biggest developed and emerging economies and its …