Transaction Isolataion with 11.1.1 server

11.1.1 promotes transaction_isolation variable to system variable, and deprecates tx_isolation.
Currently driver uses tx_isolation for reading of isolation level, and that has to be changed to transaction_isolation for new servers.
One of (current) consequences of this change is that tx_isolation tracking won't work, and thus if application changes value using SQL query, driver will return wrong value for the respective connection attribute.