Blast heard outside Iraq invasion force HQ in Qatar AS SAYLIYA CAMP, Qatar, March 23 (Reuters) - An explosion was heard on Sunday outside the Qatar headquarters of U.S.-led forces invading Iraq, apparently from a nearby industrial site, witnesses said. "We're investigating it. We just have initial reports of a sound," U.S. Marines Captain Stewart Upton, a spokesman at the U.S./UK Central Command headquarters, told Reuters. Witnesses said the explosion apparently came from warehouses outside the sprawling camp in desert land outside the capital Doha. A pall of smoke hung briefly in the air. A French journalist who was on...