DUBAI, June 1 (Reuters) - BBC Gaza correspondent Alan Johnston said in an Internet video issued by his captors on Friday that they had treated him well. "First of all, my captors have treated me very well," Johnston said on the video issued by the Army of Islam which last claimed responsibility for his kidnapping in March. The group repeated its demand on the video posted on an Islamist Web site for Britain to free Muslim prisoners, particularly the Islamist cleric Abu Qatada.