Description:
------------
proc_open.c checks if the mode parameter != "w" instead of checking the first character of the mode parameter. This prevents the mode 'wb' from working properly. 

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

$pipes = array();

$descriptor_spec = array(
    0 => array('pipe', 'rb'),
    1 => array('pipe', 'wb'),
);

$proc = proc_open('cat', $descriptor_spec, $pipes);

fwrite($pipes[0], 'Hello', 5);
fflush($pipes[0]);
fclose($pipes[0]);

$result = fread($pipes[1], 5);
fclose($pipes[1]);

proc_close($proc);

echo "Result is: ", $result, "\n";

?>

Expected result:
----------------
Result is: Hello


Actual result:
--------------
on stderr:
cat: write error: Bad file descriptor

on stdout:
Result is: