Test RepliesController#create more
Test RepliesController#create more

- Can reply to own post
- Can join post another user created
- Can reply to post owned by another user that you replied to

This fails on a4843ff and so should serve to check that
we don't have a similar problem in the future.

Marri/glowfic,Marri/glowfic,Marri/glowfic,Marri/glowfic