Sets up event handlers to add and remove a css class when the mouse is over this element
@param {String} className The class to add
@param {Function} [testFn] A test function to execute before adding the class. The passed parameter
will be the Element instance. If this functions returns false, the class will not be added.
@param {Object} [scope] The scope to execute the testFn in.
@return {Ext.dom.Element} this
function(className, testFn, scope) {
        var me = this,
            dom = me.dom,
            hasTest = Ext.isFunction(testFn);
            
        me.hover(
            function() {
                if (hasTest && testFn.call(scope || me, me) === false) {
                    return;
                }
                Ext.fly(dom, INTERNAL).addCls(className);
            },
            function() {
                Ext.fly(dom, INTERNAL).removeCls(className);
            }
        );
        return me;
    }