Simple fix for payment source.

Steps to reproduce the issue:

1. Add an order through the admin interface 2. Attempt to pay via cheque for a
user who has a credit card number stored in their profile. 3. Submit the form

This will 500, because params[:card] is set from the form on the initial page
for the radio button from the credit card profiles.

This is a simple, though incomplete fix for the issue. A proper fix would be
to change the form so that params[:card] is qualified by the payment_method
which it belongs.

There are also likely issues with multiple payment methods which support 
profiles, as there is likely to be confusion between them but this should
suffice for now.