JOHANNESBURG (Reuters) – Former South African President Nelson Mandela has recovered from a lung infection and surgery to remove gallstones that kept him in hospital for nearly three weeks, the government said on Sunday. Mandela, 94, who has been in frail health for several years, spent most of December in a Pretoria hospital – his longest stay for medical care since his release from prison in 1990. He has been receiving treatment at his Johannesburg home after he left hospital on December 26. …