Validation Fixes

Fixes several server-side validation bugs.
This will probably fail because it's comparing a timezone-naive ``datetime`` object (``datetime.now()``) to a timezone-aware ``datetime`` object (``attendee.birthdate``).  That will probably raise an exception.

If you want to get the current time, the easiest way is probably to just say ``datetime.now(UTC)`` since the ``now`` method takes an optional timezone parameter for this kind of situation.