Description:
------------
The documentation of proc_open states that passing NULL as the $env 
parameter of proc_open has the child process use the same 
environment as the current PHP process. Passing an empty array seems 
to have the same effect, even though intuitively it should give the 
child process an empty environment.

Reproduce code:
---------------
<?php
echo '<pre>';
$descriptorspec = array(
   0 => array("pipe", "r"),
   1 => array("pipe", "w"),
);
$cwd = '/tmp';
$env = array();
$process = proc_open('php', $descriptorspec, $pipes, $cwd, $env);
if (is_resource($process)) {
    fwrite($pipes[0], '<?php print_r($_ENV); ?>');
    fclose($pipes[0]);

    echo stream_get_contents($pipes[1]);
    fclose($pipes[1]);

    proc_close($process);
}


Expected result:
----------------
The script should output an (almost) empty $_ENV.

Actual result:
--------------
The script outputs the $_ENV of the parent process.