Transaction types are not consistent

On line ~164 we see this:

if ($payment_method['settings']['txn_type'] == COMMERCE_CREDIT_AUTH_ONLY ... )

COMMERCE_CREDIT_AUTH_ONLY is the string 'authorize' but the txn_type value can only be one of:

      '#options' => array(
        'AUTH' => t('Authorization only'),
        'SALE' => t('Sale'),
      ),

These should be consistent.