Make sure ActionMailer gets the SMTP settings right.

Somewhere along the way, ActionMailer became trickier to configure from an initializer (as opposed to from an `environments/*.rb` file). This fixes things to work with `avalon.yml`, but we should *probably* remove mailer configuration from `avalon.yml` and just direct people to configure ActionMailer the normal way. For one thing, this "feature" is extremely limiting in that it won't support any delivery methods other than SMTP. I can't even remember why we did it in the first place.