title: any way to format date with function field odoo?
body: <p>is there a way to display date field in different format on the view of odoo/openerp ?
  I tried using function fields as the follow lines:</p>
  
  <pre><code>     def _format_date(self, cr, uid, ids, field_name, arg, context=None):
          res = {}
          for line in self.browse(cr, uid, ids, context=context):
              res[line.id]= {
                             'date_fin':'',
                             }
              print line.id,'date ',str(line.date).replace(',','.')
               if line.date:
                   res[line.id]['date_fin']=line.date #.split()[0]
          return res
  
      _columns={ 
  'date_fin': fields.function( _format_date,method=True, string='date fin',
              store = {
                  'stock.move': (lambda self, cr, uid, ids, c={}: ids, ['sale_price_unit','product_uom_qty'], 10),
              },
          ),
          }
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>    2015-03-11 09:35:13,539 7075 ERROR db_name openerp.http: Exception during JSON request handling.
  Traceback (most recent call last):
    File "/opt/odoo/odoo/openerp/http.py", line 518, in _handle_exception
      return super(JsonRequest, self)._handle_exception(exception)
    File "/opt/odoo/odoo/openerp/http.py", line 539, in dispatch
      result = self._call_function(**self.params)
  ...
    File "/opt/odoo/odoo/openerp/models.py", line 5237, in &lt;dictcomp&gt;
      if name in fields
    File "/opt/odoo/odoo/openerp/fields.py", line 1028, in convert_to_cache
      return float_round(float(value or 0.0), precision_digits=self.digits[1])
  TypeError: float() argument must be a string or a number
  </code></pre>
  
  <p>do you have any idea of this error</p>