Tweaks to get it working under Passenger

Hi, I have a proposed set of tweaks to get this working under Passenger, including some documentation changes.

I was getting a persistent error with the confirmation process complaining about a missing reset_password_sent_at field, so I added a spec for it and tweaked the User model slightly.

Finally, I didn't commit this as I'm not sure the right way to do it, but: the most recent migration seems to be redundant if you are setting up from scratch, as the most recent version of Devise includes this field (actually the aforementioned reset_password_sent_at field).

I thought about that migration and I don't know the right way to handle it.  Those folks who are upgrading may need it for Devise to function, but it breaks the install process for those of us who set up our own database config (in my case, using Postgres) and migrate with a "from scratch" install.  Breaks the tests as well.  How to handle?