I'd like to log the email when a "validates_uniqueness_of :email" test
fails on user sign-up.
The reason for this is that I'd like to keep watch on who is trying to
use multiple accounts (for the purposes of minimizing disruptive
behaviour on my website)
So, for a new user, if they tried to first signup using an existing
email address, I'd like to have that logged in a text file somewhere.
Is there a straight-forward way to do this?