FTP backend fails location.Exists on certain windows servers

[funkyshu]

The underlying issue in the jlaffaye/ftp module is that doing a dir listing does properly recognize the date formats in some Windows ftp servers.
See jlaffaye/ftp#350

Expected behavior
We update the lib to the lastest version that includes the fix.
We should also update the dataconn.go openWriteConnection func to make a good faith effort to create a dir but to continue if the error reason is that the dir already exists which returns as 550 Cannot create a file when that file already exists.