Description:
------------
PDOStatement::execute() returns false even if the statement has been executed correctly.

I have tried it with PDO drivers for postgresql packaged with PHP version 5.1, it returns correctly true, but with version 5.2.1 it returns false. I ran into this problem while executing unit tests after an upgrade.

According to manual page should PDOStatement::execute() return true if the statement has been executed properly or false if not

Reproduce code:
---------------
try {
	$db = DBShop::getInstance();	//
	$stmt = $db->prepare('SELECT 1 AS testcolumn1, 2 AS testcolumn2');
	$count1 = $stmt->columnCount();
	$res = $stmt->execute();
	$count2 = $stmt->columnCount();
} catch (Exception $e){
	$fail[] = self::errorMsg($e, 'Unable to test columnCount()');
	break;
}
$this->assertTrue($res, 'DBStatement::execute() returned false, should be true');
$this->assertSame(2, $count2, 'DBStatement::columnCount() did not return expected value');

Expected result:
----------------
no failure in unit test:
- $res is true
- $count2 is 2

Actual result:
--------------
PHPUnit reports "DBStatement::execute() returned false, should be true", so $res is not true; but $count2 is integer of value 2, thus the statement has been executed properly