Passive server behind NAT

Hello,

Thank you for this module, i use it a lot, and it came to my attention several weeks ago, an issue regarding the declaration of ftp_pasv.

function feeds_ftp_fetcher_connect($server, $username, $password, $port) {
  if ($connect = ftp_connect($server, $port)) {
    ftp_login($connect, $username, $password);
    ftp_pasv($connect, TRUE);
    return $connect;
  }
  return FALSE;
}

I was receiving errors like: "Cannot change directory...", "Cannot retrieve file..." and so on.
My solution for my client was simple, remove ftp_pasv entirely or just use ftp_pasv($connect, FALSE);

But it's not oke for this module, i think it really needs an option for ACTIVE/PASSIVE.

Thank you.