fails:Net::FTP#size sends the SIZE command to the server
fails:Net::FTP#size returns the size of the passed file as Integer
fails:Net::FTP#size raises a Net::FTPPermError when the response code is 500
fails:Net::FTP#size raises a Net::FTPPermError when the response code is 501
fails:Net::FTP#size raises a Net::FTPTempError when the response code is 421
fails:Net::FTP#size raises a Net::FTPPermError when the response code is 550
