Fix password length for utf-8 encoded chars (http://zargony.com/2009/07/...

http://zargony.com/2009/07/24/ruby-1-9-and-file-encodings

UTF-8 chars (like é, è, ç) are encoded by a double byte in stead of a normal sized 1 byte char. So, it is better to use the bytesize of the password string in stead of the length of the string, otherwise the password strings loose some bytes at the end.