creator如何实现对一个node进行多指触控，比如双指捏合。
以前我用cocos-js的时候，有 TOUCH_ALL_AT_ONCE：
var listener =cc.EventListener.create( {
event: cc.EventListener.TOUCH_ALL_AT_ONCE,
onTouchesBegan: function (touches, event) {
cc.log('Touch Began: ’ + event);
return true;
},
onTouchesMoved: function (touches, event) {
cc.log('Touch Moved: ’ + event);
},
onTouchesEnded: function (touches, event) {
cc.log('Touch Ended: ’ + event);
},
onTouchesCancelled: function (touches, event) {
cc.log('Touch Cancelled: ’ + event);
}
});
cc.eventManager.addListener(listener, node);
而现在我翻creator文档，要求不要直接使用eventManager：
this.node.on(cc.Node.EventType.TOUCH_START, callback, this);
this.node.on(cc.Node.EventType.TOUCH_MOVE, callback, this);
this.node.on(cc.Node.EventType.TOUCH_END, callback, this);
如何实现对一个node双指捏合的操作呢？
