Description:
------------
When I write a Statement:

select 'a', tabname, 'b' from systables;

I execute the the statement with ..->query() and fetch with PDO::FETCH_ASSOC,
then the first and the third column has as name '' and the third column overwrites the first in the resulting row-array.


Test script:
---------------
<?PHP
        $db = new PDO("informix:host=<hostname>; service=<port>; database=sysmaster; server=<INFORMIXSERVER>; protocol=onsoctcp; EnableScrollableCursors=1", "informix", "<userpassword>");

        $stmt = $db->query("select 'a', tabname, 'b' from systables");
        $i = 1;

        while ($row = $stmt->fetch(PDO::FETCH_ASSOC) )
        {
                print_r($row);
                if ( $i++ > 4 ) break;
        }
?>


Expected result:
----------------
The expression columns must be named unique by example expr1, expr2, ... expr<n>.

Actual result:
--------------
Array
(
    [] => b
    [TABNAME] => systables
)
Array
(
    [] => b
    [TABNAME] => syscolumns
)
Array
(
    [] => b
    [TABNAME] => sysindices
)
Array
(
    [] => b
    [TABNAME] => systabauth
)
Array
(
    [] => b
    [TABNAME] => syscolauth
)