Track event x and y coordinates are undefined

Hi,

In debug mode on Chrome, in track.js file, they are :

``` javascript
gestureProto.x = inEvent.x; 
gestureProto.y = inEvent.y;
```

but the inEvent hasn't got x and y properties.

I think to correct this is to change by 

``` javascript
gestureProto.x = inEvent.clientX; 
gestureProto.y = inEvent.clientY;
```

Are you agree with that ?
