walk does not work on certain server

The walk function works correctly on server with standard behaviour.
for example ftp://bo.mirror.garr.it/
It outputs line formatted like this

```
modify=20081125111318;perm=adfr;size=24;type=OS.unix=symlink;unique=FE0BU200059DA;UNIX.group=0;UNIX.mode=0777;UNIX.owner=0; linux
```

But certain servers ( like ftp://ftp.packardbell.com/ ) produces output like this:

```
-rw-r--r-- 1 aokur (?) 17 Jan 5 2010 fcheck.js
```

Looking at _func (ftp *FTP) List(path string)_ I see that you first try to use _MLSD_ and if it don't work fall back to _LIST_

There are some other command that produce output more parsable than LIST.

like NLST or EPLF

Start at _func (ftp *FTP) List(path string)_ and trace the MLSD fallback to LIST handling. Compare the cited MLSD output with the Unix-style LIST output from ftp.packardbell.com, then investigate whether NLST or EPLF provides the needed information. Done means walk can handle the affected server format without breaking standard FTP listings.

Written by the indexing model from the issue text.