Agence France Presse: Demonstrators opposing the expansion of Heathrow airport climbed on to the roof of the Houses of Parliament and stayed there for three hours Wednesday, just days after a similar protest on a jet at the airport. Five activists from campaign group Plane Stupid draped two banners over the roof, one saying "No Third Runway", and the other, referring to airport operator BAA, reading "BAA Headquarters", an AFP photographer at the scene said. They ended their …