title: Odoo 7 set field value with a button
body: <p>I added a boolean field to a openerp 7 form
  at <code>on_change</code> I call my method in order to change <code>offer</code> field values on the form 
  my method returns:  </p>
  
  <pre><code>{'value': {'fieldname': 'newfieldvalue'}}
  </code></pre>
  
  <p>I want replace the boolean field with a button, but my method don't work for buttons
  that is the right return value for a button in order to change field values on the same form.</p>