fix cjk rendering bug on windows

I just use chinese to explain the problem, almost all of the chinese words can be stored in 2 bytes(http://zh.wikipedia.org/wiki/UTF-16),for example:朱[31 67],but few words is stored as 4 bytes, and editors like vim or emacs doesn't support rendering them, so I choose to ingore them, just consider the cjk word has 2 bytes.
So cell_to_char_info's return array "char", char[1] will mostly be ' ',and the real word '朱' actually is in char[0]. And i don't need to call "charsbuf = append(charsbuf, char[1])
" at this time(that's why termbox-demo2 rendering some non-need space on windows during write cjk words).
I' show you the difference after change.
![unfixed_a](https://f.cloud.github.com/assets/4971777/2267578/06380b46-9eba-11e3-9f2a-df654fcc027f.png)
![unfixed_output](https://f.cloud.github.com/assets/4971777/2267577/0637aa98-9eba-11e3-980d-6bee5b739740.png)
above is the unfix-version
![fix_a](https://f.cloud.github.com/assets/4971777/2267584/2709a460-9eba-11e3-952e-61da7d46ec95.png)
![fix_output](https://f.cloud.github.com/assets/4971777/2267585/270a0ef0-9eba-11e3-94ca-7dd488f47f02.png)
and these are fixed-version (I also changed the gocui project which is based on termbox-go)