拖拽完美版2016/4/22

 function Drag(obj)
	 {
		 obj.onmousedown=function(ev)
		 {
			var ev=ev||event;
			var disX=ev.clientX-obj.offsetLeft;
			var disY=ev.clientY-obj.offsetTop;
			if(obj.setCapture)
			{
				obj.setCapture();
			}
			document.onmousemove=function(ev)
			{
				var ev=ev||event;
				obj.style.left=ev.clientX-disX+'px';
				obj.style.top=ev.clientY-disY+'px';
			}
			document.onmouseup=function ()
			{
				document.onmousemove=null;
				document.onmouseup=null;
				if(obj.releaseCapture)
				{
					obj.releaseCapture();
				}
			}
			return false;
		 }
		
	 }