Improve keyword highlighting

Don't highlight property name whose name equals to reserved keyword.


### Before
![before](https://f.cloud.github.com/assets/554281/1846691/cb5286d0-7611-11e3-97ff-27725df27a50.png)


### After
![after](https://f.cloud.github.com/assets/554281/1846692/cdf47eca-7611-11e3-9fd1-973e8acb107a.png)