[FIX] crm: Access rights issues in contact merging

- When merging partners with fields restricted to certain groups which the user doesn't belong, an access error is raised.
  To avoid this, we only merge fields that are accessible by the user. We do so by using the method fields_get() that only returns the fields accessible by the current user.

addons/crm/base_partner_merge.py

@@ -267,8 +267,7 @@ class MergePartnerAutomatic(osv.TransientModel):
 
     def _update_values(self, cr, uid, src_partners, dst_partner, context=None):
         _logger.debug('_update_values for dst_partner: %s for src_partners: %r', dst_partner.id, list(map(operator.attrgetter('id'), src_partners)))
-
-        columns = dst_partner._columns
+        columns = dst_partner.fields_get().keys()
         def write_serializer(column, item):
             if isinstance(item, browse_record):
                 return item.id
@@ -276,8 +275,9 @@ class MergePartnerAutomatic(osv.TransientModel):
                 return item
 
         values = dict()
-        for column, field in columns.iteritems():
-            if field._type not in ('many2many', 'one2many') and not isinstance(field, fields.function):
+        for column in columns:
+            field = dst_partner._fields[column]
+            if field.type not in ('many2many', 'one2many') and field.compute is None:
                 for item in itertools.chain(src_partners, [dst_partner]):
                     if item[column]:
                         values[column] = write_serializer(column, item[column])