Former Cape Verde President Pedro Verona Pires has been awarded this year's $5m (£3.2m) Mo Ibrahim prize for good governance in Africa.The prize committee said Mr Pires, who stepped down in August, had helped make the archipelago off the West African coast a "model of democracy, stability and increased prosperity".The prize is supposed to be awarded each year to a democratically elected leader who has voluntarily left office.There has been no winner for two years.The committee said there had been no suitable candidate.The $5m award, given over 10 years, is the world's most valuable individual prize.The previous winners are Botswana's President Festus Mogae and Mozambique's Joaquim Chissano.