fix the issue   https://github.com/gabrielecirulli/2048/issues/180

fix the issue 
https://github.com/gabrielecirulli/2048/issues/180

1 .  to reproduce the bug 
![image](https://cloud.githubusercontent.com/assets/7328508/2838024/f92da672-d028-11e3-83ce-19dcbd24636e.png)
after we move up

![image](https://cloud.githubusercontent.com/assets/7328508/2838050/6df6279a-d029-11e3-847e-706488007c7e.png)

the game display game over ,instead of the "you win" message.

2. fix 
this pull request , 
outline : 
1. add an actuate call in GameManager's keepPlaying method.
2. pass keepPlaying to actuator.
3. add logic for last move won. 

see code for detail