Error messages display in a red color to improve readablity

I found it slightly annoying when the only way to indicate Mackup had encountered an error was a small normal-coloured error message that was easily lost amongst the other text. So, here are error messages in red:

![2014-04-10-115603_1280x800_scrot](https://cloud.githubusercontent.com/assets/3515754/2670725/5e9c321a-c0d1-11e3-8388-fe6dfee1f1e8.png)