title: tax vat field unique like email magento registration page
body: <p>I am trying to make the taxvat field of magento registration but i am kind of confused how do i will make it unique so everyone need to add a unique vat number . 
  here i found the email thing in accountcontroller.php</p>
  
  <pre><code> catch (Mage_Core_Exception $e) {
              $session-&gt;setCustomerFormData($this-&gt;getRequest()-&gt;getPost());
              if ($e-&gt;getCode() === Mage_Customer_Model_Customer::EXCEPTION_EMAIL_EXISTS) {
                  $url = Mage::getUrl('customer/account/forgotpassword');
                  $message = $this-&gt;__('There is already an account with this email address. If you are sure that it is your email address, &lt;a href="%s"&gt;click here&lt;/a&gt; to get your password and access your account.', $url);
                  $session-&gt;setEscapeMessages(false);
              }
              else {
                  $message = $e-&gt;getMessage();
              }
              $session-&gt;addError($message);
          }
  </code></pre>
  
  <p>Now i would like to have my taxvat field also unique like email address how i suppose to do it anybody have the code for it ?</p>