Ask to join hotfix

here's what it looks like when someone not in a group tries to interact with a discussion 

### logged in user:
![image](https://f.cloud.github.com/assets/2665886/2251976/95c8df92-9da2-11e3-8456-be9e8ebc509d.png)

---

### logged out user:
![image](https://f.cloud.github.com/assets/2665886/2252444/0631aace-9da9-11e3-9786-2e0ea854ae8b.png)


@jonlemmon this needs some design attention / sign-off