RIYADH (Reuters) - Saudi security forces arrested a suspected militant on Tuesday after five policemen were killed in a shooting spree in the kingdom's ultra-conservative Muslim heartland, the Interior Ministry said. Three policeman were shot dead at a checkpoint in the northern province of Qassim, site of several shootouts with al Qaeda-linked militants, a statement on state media said. Earlier, two policemen on patrol in the nearby town of Buraida were killed by gunshots, it added. The forces "arrested a man who was in a car", the ministry said, adding he had been wounded during his arrest. Saudi-owned Al Arabiya...