Added documentDrag option to the DragPan control and Drag handler.

When set to true, this allow pan-dragging while outside the map. 
Thanks vmx for the initial patches. r=vmx, bartvde (closes #39)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@9791 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Control/DragPan.js

@@ -34,7 +34,14 @@ OpenLayers.Control.DragPan = OpenLayers.Class(OpenLayers.Control, {
      *     panning the map again. Set this to increase dragging performance.
      *     Defaults to 25 milliseconds.
      */
-    interval: 25, 
+    interval: 25,
+    
+    /**
+     * APIProperty: documentDrag
+     * {Boolean} If set to true, mouse dragging will continue even if the
+     *     mouse cursor leaves the map viewport. Default is false.
+     */
+    documentDrag: false,
     
     /**
      * Method: draw
@@ -46,7 +53,8 @@ OpenLayers.Control.DragPan = OpenLayers.Class(OpenLayers.Control, {
                 "move": this.panMap,
                 "done": this.panMapDone
             }, {
-                interval: this.interval
+                interval: this.interval,
+                documentDrag: this.documentDrag
             }
         );
     },