Fix lineSpace bug when mix Chinese and English.

Before:
![default](https://f.cloud.github.com/assets/530060/2353960/01e20ffa-a5af-11e3-8cfd-3c79fc61ab50.png)   
After:
![fixed](https://f.cloud.github.com/assets/530060/2353961/02c2dda0-a5af-11e3-91f2-919deb1500b5.png)