draggable: second partial fix for remaining scroll issues (for the special case, subtract scrollLeft/scrollTop already in getParentOffset, so calculations become easier in _generatePosition)
draggable: second partial fix for remaining scroll issues (for the special case, subtract scrollLeft/scrollTop already in getParentOffset, so calculations become easier in _generatePosition)

GrayYoung/jQuery.UI.Extension,GrayYoung/jQuery.UI.Extension