Description:
------------
When attempting to fopen any php:// wrapper in append mode (which 
should be equivalent to writing), PHP gives the following warning 
before returning the resource:

fopen(): cannot seek on a pipe

The resource returned behaves properly.

Reproduce code:
---------------
<?php
var_dump(fopen("php://stdout", "a"));
var_dump(fopen("php://stdin", "a"));
var_dump(fopen("php://stderr", "a"));
?>

Expected result:
----------------
Warning: fopen(): cannot seek on a pipe in <...> on line 2
resource(5) of type (stream)

Warning: fopen(): cannot seek on a pipe in <...> on line 3
resource(6) of type (stream)

Warning: fopen(): cannot seek on a pipe in <...> on line 4
resource(7) of type (stream)


Actual result:
--------------
resource(5) of type (stream)
resource(6) of type (stream)
resource(7) of type (stream)