Description:
------------
Scrollable cursor support for PDO_PGSQL was introduced in PHP 5.3 (see bug #44861). Some small issues need to be ironed out, e.g. I found out that it's impossible to execute a pdo statement using a cursor twice. The current code fails as the cursor is already existing.

Reproduce code:
---------------
$pdo = new PDO("pgsql:dbname=test", 'user', 'pass', array(
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
));

$res = $pdo->prepare("SELECT (?)::int AS x", array(
        PDO::ATTR_CURSOR => PDO::CURSOR_SCROLL
));
try {
        var_dump($res->execute(array(1)));
        var_dump($res->execute(array(2)));
}  catch (Exception $e) {
        var_dump($e->getMessage());
}


Expected result:
----------------
bool(true)
bool(true)

Actual result:
--------------
bool(true)
string(94) "SQLSTATE[42P03]: Duplicate cursor: 7 ERROR:  cursor "pdo_crsr_000000000104fee8" already exists"