sftp: support rename extension for server

[kardianos]

Previously if a client makes an unsupported operation,
like a POSIX rename, it would exit the server.

Both support POSIX rename, and do not abort the connection
if there is an unsupported operation is made by the client.

[kardianos]

@eikenb Let me know if something else is needed. Previous behavior terminated loop (closed connection) when client requested an extension when using sftp.Handlers implementation. Now it will return an error if not implemented (not terminate loop) or in the case of openssh rename, just handle it like a normal rename.

Also I might add a go.mod PR if you don't mind.

[kardianos]

Ping.

[eikenb]

Hey @kardianos, thanks for the PR.

I haven't had a lot of time for this project lately, but I'm trying to make some time. I'll look at this soon.

[eikenb]

Actually, I'm already looking at this. Realized when reading through #299 that we didn't handle extended packets in either server and was looking into fixing that.

[eikenb]

So I think I'm just going to merge this. It works and doesn't conflict (much) with the other 2 extended packet related PRs. I'm going to pull in all 3 and then get things working and go from there. I'm going to do the merge locally as there will be a few conflicts that I'd prefer to resolve locally vs. githuts tool. Thanks.

[eikenb]

Merged.
I rebased before merging, which changed the ids and so it didn't auto-close.

[kardianos]

Thanks! (I understand about having little time :) )