Make the warning message a little nicer looking

Just make the broken Add-on warning a little nicer.

Warning I have not tested this yet due to some problems with the rewrite rules, but in theory it should work :)

![broken](https://f.cloud.github.com/assets/1050512/1656107/92df12e6-5b6d-11e3-8a27-355f66eb6fbc.jpg)