VOTERS headed to the polls yesterday in the tiny but strategically important Horn of Africa nation Djibouti, with President Ismael Omar Guelleh widely expected to win a fifth term and extend his 21-year-long rule. The desert nation of less than one million people lies on one of the world's busiest shipping routes, the Gulf of Aden, and hosts U.S., Chinese, and French military bases, letting it punch above its weight. Guelleh, 73, is one of Africa's longest-ruling leaders. He was picked to succeed his uncle, Hassan Gouled Aptidon, who led the country to independence from France in 1977. Guelleh faces…