Escape linter messages

Some linters return text containing special characters that need to be escaped.

Before:

![screen shot 2014-10-02 at 16 29 54](https://cloud.githubusercontent.com/assets/1759837/4493411/3affe96c-4a49-11e4-820f-8a2ec102cd49.png)

After:

![screen shot 2014-10-02 at 16 30 56](https://cloud.githubusercontent.com/assets/1759837/4493412/3b01e0d2-4a49-11e4-9fa4-b38742288d12.png)