Description:
------------
PDO::setAttribute must raise an error if an incorrect value is passed for the 
attribute but it doesn`t, see example

Test script:
---------------
$pdo = new \PDO('mysql:host=127.0.0.1;dbname=db', 'login', 'pass');
$pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::CASE_NATURAL);

Expected result:
----------------
Warning: Incorrect value for PDO::ATTR_ERRMODE

Actual result:
--------------
nothing - just empty screen