try to properly calculate visual width of multibyte characters

before:

![screen shot 2014-11-14 at 4 17 59 pm](https://cloud.githubusercontent.com/assets/39759/5042516/d5281b9e-6c19-11e4-86b0-ffaea7e8d166.png)

after:

![screen shot 2014-11-14 at 4 17 35 pm](https://cloud.githubusercontent.com/assets/39759/5042517/d7dfd110-6c19-11e4-8233-6f58840b7b4a.png)