Add python 3 support

sale.py

@@ -13,10 +13,9 @@ from trytond.wizard import Wizard, StateView, StateTransition, Button
 __all__ = ['Sale', 'SalePaymentForm', 'WizardSalePayment',
     'WizardSaleReconcile']
 
-__metaclass__ = PoolMeta
-
 
 class Sale:
+    __metaclass__ = PoolMeta
     __name__ = 'sale.sale'
     payments = fields.One2Many('account.statement.line', 'sale', 'Payments')
     paid_amount = fields.Function(fields.Numeric('Paid Amount', readonly=True),

statement.py

@@ -10,15 +10,16 @@ from decimal import Decimal
 __all__ = ['Journal', 'Statement', 'Line', 'OpenStatementStart',
     'OpenStatementDone', 'OpenStatement', 'CloseStatementStart',
     'CloseStatementDone', 'CloseStatement']
-__metaclass__ = PoolMeta
 
 
 class Journal:
+    __metaclass__ = PoolMeta
     __name__ = 'account.statement.journal'
     devices = fields.One2Many('sale.device', 'journal', 'Devices')
 
 
 class Statement:
+    __metaclass__ = PoolMeta
     __name__ = 'account.statement'
     users = fields.Function(fields.One2Many('res.user', None, 'Users'),
         'get_users', setter='set_users', searcher='search_users')
@@ -58,6 +59,7 @@ class Statement:
 
 
 class Line:
+    __metaclass__ = PoolMeta
     __name__ = 'account.statement.line'
     sale = fields.Many2One('sale.sale', 'Sale', ondelete='RESTRICT')
 

user.py

@@ -8,10 +8,10 @@ from trytond.pyson import Eval
 
 
 __all__ = ['User']
-__metaclass__ = PoolMeta
 
 
 class User:
+    __metaclass__ = PoolMeta
     __name__ = "res.user"
     sale_device = fields.Many2One('sale.device', 'Sale Device',
             domain=[('shop', '=', Eval('shop'))],