Better mousewheel/touchpad behavior for zooming

The navigation control gets better defaults, and the MouseWheel handler
gets a new maxDelta option, which can be used to avoid huge zoom level
jumps on heavy wheel/pad movements.

lib/OpenLayers/Control/Navigation.js

@@ -77,7 +77,9 @@ OpenLayers.Control.Navigation = OpenLayers.Class(OpenLayers.Control, {
     /**
      * Property: mouseWheelOptions
      * {Object} Options passed to the MouseWheel control (only useful if
-     *     <zoomWheelEnabled> is set to true)
+     *     <zoomWheelEnabled> is set to true). Default is no options for maps
+     *     with fractionalZoom set to true, otherwise
+     *     {cumulative: false, interval: 50, maxDelta: 6} 
      */
     mouseWheelOptions: null,
 
@@ -208,10 +210,15 @@ OpenLayers.Control.Navigation = OpenLayers.Class(OpenLayers.Control, {
                     {map: this.map, keyMask: this.zoomBoxKeyMask});
         this.dragPan.draw();
         this.zoomBox.draw();
+        var wheelOptions = this.map.fractionalZoom ? {} : {
+            cumulative: false,
+            interval: 50,
+            maxDelta: 6
+        };
         this.handlers.wheel = new OpenLayers.Handler.MouseWheel(
-                                    this, {"up"  : this.wheelUp,
-                                           "down": this.wheelDown},
-                                    this.mouseWheelOptions );
+            this, {up : this.wheelUp, down: this.wheelDown},
+            OpenLayers.Util.extend(wheelOptions, this.mouseWheelOptions)
+        );
         if (OpenLayers.Control.PinchZoom) {
             this.pinchZoom = new OpenLayers.Control.PinchZoom(
                 OpenLayers.Util.extend(