Attempts to establish a passive connection to the FTP server.

Return value

Expected type: Boolean
Description: True if successful, false otherwise

• See http://www.slacksite.com/other/ftp.html for a detailed explanation on passive mode.
• Example: $package_ftp->passive();
• Checks to make sure a connection has actually been made first.
• Sends the PASV command to the server and waits 5 seconds for a response.
• Checks for a 227 (Entering passive mode) response code
• Sets a 'bad_response' error if the response code isn't 227 or the IP/Port info isn't valid
• Returns false if there's no connection or the response wasn't valid
• Parses IP/port info and puts it in "pasv" array for later use
• Returns true if successful