Bug 1090990: Fix unicode error for emails with non-ascii domains.

This fixes the unicode decode error, but validation will still fail for emails
with non-assci user components (before @). Open question in the bug on what we should
consider valid here based on what ET considers valid.
I don't think modifying the value in a validation method is a good idea. I'm not sure if adding an extra "perpare_email" method is the best fix, though. It's a bit awkward.