We take the comment as a parameter instead of the user, since usually
people reply to comments and not to users.
We also remove one database query after the browser has started, since
we can use `debate_path(debate)`. It's also more clear why we're using
`debate_path` in the test; before these changes, we had to enter the
`reply_to` method to realize that we were replying on a debate.
9f926de54e