By Duncan Miriri NAIROBI (Reuters) – Kenya’s former president Mwai Kibaki, who has died aged 90, ushered in economic reforms and a new constitution but failed to deliver on promises to combat graft and his tenure was marred by a disputed re-election which led to deadly violence. A British-educated economist, Kibaki’s unflappable demeanour concealed political guile that finally propelled him to the presidency after four decades as lawmaker, government minister and then vice president to his predecessor, Daniel arap Moi. His landslide win in 2002 upset Moi’s handpicked successor. Kibaki, in a wh…