[session] explicitly take Connection object in close_cnx Now that ClientConnection explicitly reference and use the Connection object we do not need to use connectionid here. We can safely change this signature, ClientConnection is the only use of close_cnx for now.

[session] drop the Session._clear_cnx_storage method It is just cnx.clear() now.

[session] wrap too long line Too long line is too long. (Confucius 503 BC)

[session] gather close_cnx with get_cnx and set_cnx They do the same kind of operation and deserve to be grouped together.

[client-connection] remove the _srv_cnx usage It does not do anything special now that we use explicite Connection object with automatic cnx_set handling.

[client-connection] explicitly check that the client-connection is open The check is also perform by the _srv_cnx property. But we do not need those property anymore.

[client-connection] handle the lack of connection id while not open the connection id is computed at opening and forgotten when closing. We can't rely on it in various messages … like the "connection closed" exception.

[connection] transparent cnx_set handling Connection object while take cares of there cnxset themself (as dbapi connection does). The ``set_cnxset`` and ``free_cnxset`` operation are still available for backward compatibility purpose. The ``_auto_free_cnx_set`` is introduced to handle mixed usage. A new context manager ``connection.ensure_cnx_set`` is added for code that access ``cnx.cnxset`` directly and are not wrapped in any specific ``Connection`` method. A ``_with_cnx_set`` decorator is used on all Connection method that need a cnxset.