title: TypeError: ... is not JSON serializable
body: <p>Here is my error</p>
  
  <pre><code>  File "/usr/share/pyshared/simplejson/encoder.py", line 202, in default
      raise TypeError(repr(o) + " is not JSON serializable")
  TypeError: browse_record(bpl.division.n.registration, 1) is not JSON serializable
  </code></pre>
  
  <p>Here is my relation mapping table</p>
  
  <pre class="lang-cs prettyprint-override"><code>class company_estate_division(osv.osv):
      _name = 'bpl.company.estate.division'
      _description = 'bpl company estate division mapping'
      _columns = {
          'bpl_estate_id': fields.many2one('bpl.estate.n.registration', 'Estate', select=True),
          'bpl_division': fields.related('bpl_estate_id', 'divisions', type='char', string='Estate &amp; Division'),
          }
  </code></pre>
  
  <p>And here shows my division and estate model classes.</p>
  
  <pre class="lang-cs prettyprint-override"><code>class estate_new_registration(osv.osv):
      _name = "bpl.estate.n.registration"
      _description = "Estates"
      _columns = {
          'name': fields.char('Estate Name', size=128, required=True),
          'company_id': fields.many2one('res.company', 'Company Name', select=True),
          'divisions': fields.one2many('bpl.division.n.registration', 'estate_id', 'Division')
      }
  class division_new_registration(osv.osv):
      _name = "bpl.division.n.registration"
      _description = "Divisions"
      _columns = {
          'name': fields.char('Division Name', size=128, required=True),
          'estate_id': fields.many2one('bpl.estate.n.registration', 'Estate Name', select=True),
      }
  </code></pre>
  
  <p>I need to map <code>company</code> to <code>estates</code>. (company one-to-many estates)
  I think using related fields is easier than others for this mapping. Please help.</p>