patch for improved mousedragging. We were able to test this on my eeepc

and get a very obvious speedup in performance. This adds a configurable
'interval' to the dragpan control (and an interval to the 'drag' control,
defaulting to 0px). Patch put together by tcoulter. (Closes #1509) 


git-svn-id: http://svn.openlayers.org/trunk/openlayers@7608 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Control/DragPan.js

@@ -28,14 +28,27 @@ OpenLayers.Control.DragPan = OpenLayers.Class(OpenLayers.Control, {
      */
     panned: false,
     
+    /**
+     * Property: interval
+     * The number of milliseconds that should ellapse before
+     * panning the map again. Set this to increase dragging performance.
+     * Defaults to 25 milliseconds.
+     */
+    interval: 25, 
+    
     /**
      * Method: draw
      * Creates a Drag handler, using <panMap> and
      * <panMapDone> as callbacks.
      */    
     draw: function() {
-        this.handler = new OpenLayers.Handler.Drag(this,
-                            {"move": this.panMap, "done": this.panMapDone});
+        this.handler = new OpenLayers.Handler.Drag(this, {
+                "move": this.panMap,
+                "done": this.panMapDone
+            }, {
+                interval: this.interval
+            }
+        );
     },
 
     /**