Strip out ^[[2K and ^[[0G in tmux output

`^[[2K` is an escape code, which means "erase entire current line" and should not
be included in the output. `^[[0G` is another escape code. I could not find out
its meaning, but it clutters up the output as well. See the screenshot for an "before" example.

![example](https://cloud.githubusercontent.com/assets/2971615/3888764/0b3d8ed6-2204-11e4-8621-ebb384b04587.png)