Description:
------------
Support for the SERIAL datatype using PDO

Reproduce code:
---------------
$db = new PDO( 
"informix:host=xeo;service=1526;database=stores_demo;server=ol_xeo;protocol=olsoctcp;EnableScrollableCursors=1;DB_LOCALE=EN_US.8859-1"/* connection string */ , 
"informix"/* user */ , 
"informix"/* password */); 

$insstmt = 'insert into customer(customer_num, fname, lname, company) values(?, ?, ?, ?);'; 

$stmt = $db->prepare($insstmt); 

$dataarray = array('0', 'Jean Georges', 'Perrin', 'None'); 
$result = $stmt->execute($dataarray); 

if ($result == true) { 
echo ("Row successfully insterted, customer #" . $db->lastInsertId()); 
}

Expected result:
----------------
PDO::lastInsertId() should *NOT* return: 
SQLSTATE[IM001]: Driver does not support this function: driver does not support lastInsertId() in xxx

It should return the correct value of the SERIAL.