title: OpenERP file downloads with no extension
body: <p>I have created a file and stored in database. When I download the file, it has no extension. Also, the downloaded file comes with name "className_ID" instead of the File name specified.</p>
  
  <p><strong>Here is my python code</strong></p>
  
  <pre><code>class dev_history(osv.osv):    
  _name = 'dev.history'
  _order = 'id desc'
  
  _columns = {   
      'doc_file':fields.binary('Document'),
      'doc_name' : fields.char('Name',size=32),
      }
  _defaults = { 'doc_name': "Device History.doc", }
  
  dev_history()
  </code></pre>
  
  <p><strong>XML Code:</strong></p>
  
  <pre><code>&lt;field name="doc_file" string="File" readonly="1" filename='doc_name'  attrs="{'invisible':[('doc_name','=','')]}"/&gt;
  &lt;field name="doc_name" readonly="1" invisible="1" colspan="2" attrs="{'invisible':[('doc_file','=','')]}"/&gt;
  </code></pre>
  
  <p>Am I doing anything wrong? Please help!</p>