title: add a attribute to sales/order model in magento in product environment
body: <p>I want add a attribute to order,the following steps is works in the test environment,but not works in product environment ,there is a difference between the two environments,the product env is  implement database Master-slave separation,but test env not .
  steps: <br>
  1.because in the database table *core_resource*  is <br>
  <code>code;| version</code><br><code>sales_setup|0.9.40</code><br>
  so I modified the file /app/code/core/Mage/Sales/etc/config.xml<br>
       <code>&lt;modules&gt;</code>  <br> 
       <code>&lt;Mage_Sales&gt;</code> <br>
       <code>&lt;version&gt;0.9.41&lt;/version&gt;</code> <br>
       <code>&lt;/Mage_Sales&gt;</code> <br>
       <code>...</code><br>
       <code>&lt;/modules&gt;</code>  <br>
  2.add a file /app/code/core/Mage/Sales/sql/sales_setup/mysql4-upgrade-0.9.40-0.9.41.php <br>
  the content is :<br>
  <code>$installer = $this;</code> <br>
  <code>$installer-&gt;addAttribute('order', 'prx', array(</code><br>
  <code>'type'          =&gt; 'varchar',</code><br>
  <code>'backend_type'  =&gt; 'varchar',</code><br>
  <code>'frontend_input' =&gt; 'varchar',</code><br>
   <code>'is_user_defined' =&gt; true,</code><br>
   <code>'label'         =&gt; 'prx',</code><br>
  <code>'visible'       =&gt; true,</code><br>
   <code>'required'      =&gt; false,</code><br>
   <code>'user_defined'  =&gt; false,</code><br>
   <code>'searchable'    =&gt; false,</code><br>
  <code>'filterable'    =&gt; false,</code><br>
  <code>'comparable'    =&gt; false,</code><br>
  <code>'default'       =&gt; ''</code><br>
  <code>));</code><br></p>
  
  <p>who can tell me why,thanks!</p>
  
  <p>if the script is just add a record in the table <strong>*eav_attribute*</strong>?can I add the record by a sql script instead?</p>