Sitting in a building made from used tyres, plastic bottles and old sneakers, Cambodian student Roeun Bunthon jots down notes during an English lesson at the "Rubbish School" where tuition is paid for with trash instead of cash.In return, needy kids like Bunthon, a former street beggar, can take computer, mathematics and language classes - and learn the value of reducing waste in a notoriously polluted country where recycling is nearly non-existent."I've stopped begging...