Description:
------------
Opening the php://output stream seams to flag the headers as sent, event if output buffering is on. Consequently, any call to header() fails where it shouldn't.

Affects any extension that uses streams.


Reproduce code:
---------------
<?php

ob_start();
$h = fopen('php://output', 'wb');
fclose($h);
ob_end_clean();

header('X-Foo: bar');

?>

Or

<?php

ob_start();
$dom = new DOMDocument;
$dom->save('php://output');
ob_end_clean();

header('X-Foo: bar');

?>

Expected result:
----------------
blank page

Actual result:
--------------
Warning: Cannot modify header information - headers already sent in C:\[...]\test.php on line 8