BY MARK HOSENBALL AND SYLVIA WESTALL (Reuters) – Islamic State militants fighting in Iraq and Syria posted a video on Friday that appeared to show the beheading of British aid worker Alan Henning, triggering condemnation by the British and U.S. governments. The footage on YouTube, highlighted on pro-Islamic State Twitter feeds, showed a bearded man in an orange jumpsuit kneeling next to a black-clad man in arid scrubland, similar to past Islamic State beheading videos of two Americans […]