fix #1238: remove left gravity in edit comment text box

fix #1238: remove left gravity in edit comment text box

Before:
![screencap-2014-06-19t12-33-39 0200](https://cloud.githubusercontent.com/assets/40213/3326405/52576170-f79d-11e3-9235-884b72e17fa4.png)


After:
![screencap-2014-06-19t12-34-06 0200](https://cloud.githubusercontent.com/assets/40213/3326404/525529f0-f79d-11e3-82f4-94c34f4fe991.png)