Robson Braga Araujo filed bug report #1739100

(http://curl.haxx.se/bug/view.cgi?id=1739100) that mentioned that libcurl
could not actually list the contents of the root directory of a given FTP
server if the login directory isn't root. I fixed the problem and added three
test cases (one is disabled for now since I identified KNOWN_BUGS #44, we
cannot use --ftp-method nocwd and list ftp directories).