Changed #visible_to_the_public to include 'Mostly Private' groups

'Mostly Private' groups were not showing up on the group index.  Tests included in group_spec

Before

![image](https://f.cloud.github.com/assets/4204461/2432291/fc71ee12-ad5d-11e3-934a-94d3d677c5ae.png)

After

![image](https://f.cloud.github.com/assets/4204461/2432293/1d766aca-ad5e-11e3-9d35-66a051e768c8.png)