TIM COCKS LADYSMITH Black Mambazo sang their warm-hearted choral harmonies in honour of peace icon Nelson Mandela, with a 45-minute forced intermission caused by one of the power cuts that have become a part of daily life in South Africa. The concert in Johannesburg's main theatre, a day before U.N.-declared Mandela Day, his birthday, celebrated the life of the man who steered South Africa from the manacles of apartheid to multi-racial democracy while narrowly avoiding a civil war. "Madiba has been an inspiration for us," Sibongiseni Shabalala, band member and son of the band's late founder Joseph Shabalala, said, using…