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/2665886/2251973/91c9a67e-9da2-11e3-90e2-bbb5aa3c06e7.png)

@jonlemmon this needs some design attention / sign-off