add smooth drag panning to yahoo layer. the trinity is united. killer props to cr5 for digging through and finding these. ladies and gentlemen, you now have *no*excuse* for not using openlayers. smooth and sexy GYM commercial layers. (Closes #1163)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@5230 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Yahoo.js

@@ -92,6 +92,13 @@ OpenLayers.Layer.Yahoo = OpenLayers.Class(
             this.mapObject = new YMap(this.div, this.type, size);
             this.mapObject.disableKeyControls();
             this.mapObject.disableDragMap();
+
+            //can we do smooth panning? (moveByXY is not an API function)
+            if ( !this.mapObject.moveByXY || 
+                 (typeof this.mapObject.moveByXY != "function" ) ) {
+
+                this.dragPanMapObject = null;
+            }                
         } catch(e) {}
     },
 
@@ -248,6 +255,20 @@ OpenLayers.Layer.Yahoo = OpenLayers.Class(
         return this.mapObject.getCenterLatLon();
     },
 
+    /**
+     * APIMethod: dragPanMapObject
+     * 
+     * Parameters:
+     * dX - {Integer}
+     * dY - {Integer}
+     */
+    dragPanMapObject: function(dX, dY) {
+        this.mapObject.moveByXY({
+            'x': -dX,
+            'y': dY
+        });
+    },
+    
     /** 
      * APIMethod: getMapObjectZoom
      *