The FTP server (ProFTPD 1.3.5a) returns some file and folder names not properly encoded in UTF-8, when requesting with FTP command "MLSD" and "OPTS UTF8 ON".
To access I need to send them back to the server exactly as they came (bytes) with ftp.sendcmd(b"CWD" + path_bytes).

This results in an exception:
 File "C:\Python34\lib\ftplib.py", line 190, in putline
 line = line + CRLF
 TypeError: can't concat bytes to str

Sadly this makes ftplib only support sending of UTF-8 commands and file names. So I need to work around with my own version of "sendcmd" for now.

"ftplib.sendcmd()" should handle bytes and strings (UTF-8).