Fix Oracle not showing error number and messages

I've had problems with CI 2.1.3 where any error in queries to an Oracle database would just show "Database error has occured" but didn't show what error.

While examining system/drivers/oci8/oci8_driver.php I saw the oci_error was being sent the connection instead of the statement.

Also my code has a fix for the following known issue : https://github.com/EllisLab/CodeIgniter/wiki/Oracle:Known-Issues