Fix drag pan for rotated maps

demos/side-by-side/index.html.in

@@ -67,7 +67,6 @@
         </table>
         <p><b>Notes:</b> The two maps share the same center, resolution, rotation and layers.  Currently the DOM map does not support rotation.</p>
         <p><b>Console tips:</b> If you want to play around with the API in the console, first make sure that you're using the <a href="simple-optimizations.html">simple optimizations version</a> of this demo, then open a console and experiment with the <code>domMap</code>, <code>webglMap</code> and <code>layer</code> variables in the console. The source code is in <a href="side-by-side.js">side-by-side.js</a>.</p>
-        <p><b>Known bugs:</b> When the map is rotated, panning on the WebGL map doesn't work as expected.</p>
         <script src="@SRC@" type="text/javascript"></script>
     </body>
 </html>

src/ol/interaction/dragpan.js

@@ -1,5 +1,3 @@
-// FIXME cope with rotation
-
 goog.provide('ol.interaction.DragPan');
 
 goog.require('ol.Coordinate');
@@ -26,8 +24,12 @@ goog.inherits(ol.interaction.DragPan, ol.interaction.Drag);
 ol.interaction.DragPan.prototype.handleDrag = function(mapBrowserEvent) {
   var map = mapBrowserEvent.map;
   var resolution = map.getResolution();
+  var rotation = map.getRotation();
   var delta =
       new ol.Coordinate(-resolution * this.deltaX, resolution * this.deltaY);
+  if (map.canRotate() && goog.isDef(rotation)) {
+    delta.rotate(rotation);
+  }
   this.pan(map, delta, this.startCenter);
 };