ROLI SRIVASTAVA  THE death of an eight-year-old boy whose parents worked as bonded labourers has triggered demands for authorities to crack down on thousands of other suspected cases in nearby villages in central India. Debt bondage is India's most common form of slavery despite being outlawed four decades ago, and millions of bonded labourers work in fields, brick kilns and rice mills to clear loans. Police said the boy's parents, who were repaying a 25,000-rupee loan by working on their employer's farms for five years without pay, lived in a "polythene hut" and were assaulted when they asked for money…