Workaround for "HTTP Error" during upload.

$_COOKIE has precedence over $_POST when $_REQUEST gets constructed,
so if flash uploader sends a bad PHPSESSID cookie, the bad
$_COOKIE['PHPSESSID'] was present in $_REQUEST, not the correct
$_POST['PHPSESSID']. Changing $_REQUEST to $_POST in _config.php
fixes this problem.
Merge branch 'master' of https://github.com/lazyeugene/Uploadify