Fix at-door payment options

Fixes two problems: one in registration.py that tries to access Attendee.get, and one referencing a non-existent KLUDGE_PAYMENT_OPTS

Fixes #562.
Haha, I forgot about this!  For anyone wondering, someone (who shall remain nameless :P) asked me to make a few changes to registration on the Tursday of the week of MAGFest last year, so I threw together a temporary list of payment options which was only used here called ``KLUDGE_PAYMENT_OPTS`` as a temporary measure.