A man walks gingerly over a small field in rural Cambodia, pushing a lawnmower-like contraption that deploys ground-penetrating radar to unearth clues of mass graves.The pilot project is twinning technology and fieldwork to locate remains of victims of the Khmer Rouge, the ultra-Maoist regime whose quest to build an agrarian utopia from 1975 to 1979 left an estimated two million Cambodians dead.Hacked to death, starved, overworked or ravaged by illness, their bodies were dumped in hastily dug