When a Hundred is a Fifty   By Pranay Gupte   Sachin Tendulkar of India cracked his 50 th Test century in South Africa on Sunday evening, a record that’s unlikely to be broken any time soon. His nearest rivals – Ricky Ponting of Australia, with 39 centuries – and Jacques Kallis of South Africa, with 38 centuries – simply do not have Tendulkar’s stamina and steadiness. Moreover, the 36-year-old Indian batsman isn’t done yet – who kn...