Mercurial repository info in agnoster theme

I modded agnoster theme to add the same functionality it has for git. It displays the status of the mercurial repository, if any in cwd.
![Capture d e cran 2013-01-20 a 13 17 11](https://f.cloud.github.com/assets/353843/81147/6cf91e16-62fb-11e2-948d-d1f6909a1528.png)