do not raise error if setting is not changed

tiramisu/storage/postgres/storage.py

@@ -35,6 +35,8 @@ class Setting:
         self.dsn = 'postgres:///tiramisu?host=/var/run/postgresql/&user=tiramisu'
 
     def __setattr__(self, key, value):
+        if hasattr(self, key) and getattr(self, key) == value:
+            return
         if POOL is not None:  # pragma: no cover
             raise Exception(_('cannot change setting when connexion is already '
                               'opened'))