TIM COCKS NIGERIANS will vote in what could be their most credible and close electoral contest since military rule ended nearly a quarter of a century ago - and the first in which a presidential candidate who isn't from one of the two main parties stands a chance. Former Lagos governor Bola Tinubu of the ruling All Progressives Congress (APC) faces Atiku Abubakar of the main opposition Peoples Democratic Party (PDP) and Peter Obi, a wild-card candidate who defected from the PDP to the smaller Labour Party and now leads in at least five opinion polls. Obi, 61, has used…