Clean up Opera setDragImage patch

Issue #1166

Author: marijnh

lib/codemirror.js

@@ -169,15 +169,6 @@ window.CodeMirror = (function() {
     // Used for measuring wheel scrolling granularity
     d.wheelDX = d.wheelDY = d.wheelStartX = d.wheelStartY = null;
 
-    //opera setDragImage hack
-    if (opera) {
-      var img = elt('img');
-		  img.width = '1';
-		  img.height = '1';
-		  img.setAttribute('style','position:fixed; top:0; left:0; right:0');
-	  	d.wrapper.appendChild(img);
-    }
-
     return d;
   }
 
@@ -1621,9 +1612,17 @@ window.CodeMirror = (function() {
 
     // Use dummy image instead of default browsers image.
     // Recent Safari (~6.0.2) have a tendency to segfault when this happens, so we don't do it there.
-    var img = opera ? cm.display.wrapper.getElementsByTagName('img')[0] : elt('img');
-    if (e.dataTransfer.setDragImage && !safari)
+    if (e.dataTransfer.setDragImage && !safari) {
+      var img = elt("img", null, null, "position: fixed; left: 0; top: 0;");
+      if (opera) {
+        img.width = img.height = 1;
+        cm.display.wrapper.appendChild(img);
+        // Force a relayout, or Opera won't use our image for some obscure reason
+        img._top = img.offsetTop;
+      }
       e.dataTransfer.setDragImage(img, 0, 0);
+      if (opera) img.parentNode.removeChild(img);
+    }
   }
 
   function setScrollTop(cm, val) {