Australian Broadcasting Corporation: MARK COLVIN: Governments that were quick to switch to biofuels are just as quickly having to think again. Biofuels were promoted as an effective weapon in the battle against climate change, but some blame the increased demand for them for a world crisis in the cost of food. Earlier this month a doubling in the price of rice caused riots in Egypt and Haiti, and the World Bank has warned the increased cost of food will push 100-million people deeper into poverty. But aid …