Add support for FXP (FTP to FTP copy)

I like the idea; it's surely more efficient to copy directly from FTP host to FTP host.

As I said in a comment in ticket #6, I would like to experiment with FXP in the mirror script. (Hm, I see that FXP can useful in other situations than mirroring trees).

A workaround (beside the one you mention) for your problem might be to run a regular up/download on one of the FTP hosts itself. However, I'm aware that this has the downside that you need shell access to that host or know someone who has shell access and puts your script on that host.

Do you ask out of curiosity, or have you already run into a situation where you would like to use FXP?

Another question: Did you deliberately classify the ticket's priority as "major" or did you just keep the default value? Is the priority "major" from your point of view or needs?

Hi Stefan, thanks for you offering such a great library!

For the ticket's priority, I just leave it as the default value, I'm sorry I'm not very familar with Trac.

I agree that not everyone need this feature, even some famous FTP client (eg, FileZilla?) don't support it, but it really useful for ftp administrators. At sometimes, the ftp administrators can only access the server via ftp protocol, so many operations depend on the ftp client tool (or scripts).

For my situation, I run a series of ftprush script to syncronize a ftp server from several upstream servers everyday. But I like python more and would like to rewrite it to a python script for more flexibility.

On the other hand, I think it's really a low-level operation which doesn't like things such as downloadtree() which just a handy goodie. You need to call the _session attribute and send raw ftp command to implement it, I think it break the encapsulation in some sense. That's why I hope it can be supported directly by the library.

Thanks again for your reply:)