Add FTP active mode capability

[gbourel]

Add a connection option which allows to use FTP active mode instead of default passive behavior.

The passive option on connect allows to select FTP mode between active or passive:

• default value is set to true in order to keep same behavior when this option isn't set.
• when passive is set to true, this FTP client uses active mode, by using the PORT command to trigger a socket connection set up from the FTP server. In order to ensure IP address which should be reached for this connection the activeIp option may be set to define which IP the FTP server must use when initiating this connection.

[748890753yiyi]

eg:
var ftpClient = new ftp();
ftpClient.connect({
host: '',
port: 21,
user: '',
password: '',
passive:false,
activeIp:""
});
ftpClient.on('ready', function () {
console.log("ready");//this is right
ftpClient.list(dir, function (err, list) {//This list function has no return value
if (err) throw err;
console.dir(list);
ftpClient.end();

    });
});

I use this active mode in my ftp module, but ftpClient.list function has no return value, ready can be show,

[lroal]

Any news on active mode ?

[lracicot]

Can this be merged? We need this on some networks.

[rk-7]

Anyone maintaining this PR?