This prefab was created by newbie AKA theguyformerlyknowasnewbie AKA newernewbie. Should you wish to include this prefab in your map credit should be awarded to the author.
Thanks to smoogle who gave me the idea. This is based on his prefab which is at http://prefabs.gamedesign.net/sub_category.php3?sub_category_id=25&category_id=5&game_id=3&start=5&total_num=10