title: Undefined class constant 'CHECK_USE_CHECKOUT'
body: <p>I upgraded magento from version 1.9.1.1 to 1.9.2.1. The checkout process always fails and redirects back to thee cart page. This is the Error I found in Apache's error log:</p>
  <pre><code>PHP Fatal error:  Undefined class constant 'CHECK_USE_CHECKOUT' in
  /var/www/app/code/local/Lotusbreath/OneStepCheckout/Model/Type/Onepage.php 
  on line 108, referer: http://www.websitename.com/onestepcheckout/
  </code></pre>
  <p>I thought the checkout extension was faulty, so I replaced it with the original Magento checkout template, the same error appears:</p>
  <pre><code>PHP Fatal error:  Undefined class constant 'CHECK_USE_CHECKOUT' in 
  /var/www/app/code/core/Mage/Checkout/Model/Type/Onepage.php on line 653,
  referer: http://www.website.com/checkout/onepage/
  </code></pre>
  <p>I checked both PHP files for the CHECK_USE_CHECKOUT and indeed, it's not defined there. Question is, this used to work fine before this. I am not sure if this update broke something or is it the recent patch fix I have applied. I tried reverting the patch but that didn't work either.</p>
  <p>This is the snippet from the PHP file Onepage.php that contains the CHECK_USE stuff:</p>
  <pre><code>$data['checks'] = Mage_Payment_Model_Method_Abstract::CHECK_USE_CHECKOUT
          | Mage_Payment_Model_Method_Abstract::CHECK_USE_FOR_COUNTRY
          | Mage_Payment_Model_Method_Abstract::CHECK_USE_FOR_CURRENCY
          | Mage_Payment_Model_Method_Abstract::CHECK_ORDER_TOTAL_MIN_MAX
          | Mage_Payment_Model_Method_Abstract::CHECK_ZERO_TOTAL;
  </code></pre>
  <p>Is this the reason payments are failing and redirecting back to the cart page? If so, how would I go about fixing this?</p>