update rails version
facebook/rails_util.rb: since the code might be used up, we favor ours

so that we don't have to ask facebook to update access token every time.
facebook/rails_util.rb: we still need to update our fbs from cookie!

this is how new facebook cookie works, since we can't simply get
the access token from the cookie, we need to exchange it with
the code. that means, we need our own persistent storage for
the access token, not relying on what facebook gave us.