Add missing domain parent = False for vat taxes on party

tax.py

@@ -789,12 +789,14 @@ class Party(OSV):
     vat = fields.Property(type='many2one',
             relation='account.tax', string='VAT',
             group_name='Accounting Properties', view_load=True,
-            domain="[('group.code', '=', 'vat'), ('company', '=', company)]",
+            domain="[('group.code', '=', 'vat'), ('company', '=', company), " \
+                    "('parent', '=', False)]",
             help='This tax will be used, instead of the default VAT.')
     supplier_vat = fields.Property(type='many2one',
             relation='account.tax', string='Supplier VAT',
             group_name='Accounting Properties', view_load=True,
-            domain="[('group.code', '=', 'vat'), ('company', '=', company)]",
+            domain="[('group.code', '=', 'vat'), ('company', '=', company), " \
+                    "('parent', '=', False)]",
             help='This tax will be used, instead of the default VAT ' \
                     'for supplier invoices.')