Updated PDO error handling chapter with new example and added note to reflect PDO::__construct behavior.

This fixes Bug #63845 in that a note is added to inform the user that PDO::__construct will always throw an exception if the connection fails.
A new example is also added to reflect that even when the PDO::ATTR_ERRMODE is set in the constructor, and the connection fails, a PDOException will still be thrown.


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@329077 c90b9560-bf6c-de11-be94-00142212c4b1