Crappy SCP support

[willnx]

So, OpenSSH supports scp on the sink by executing something like this:
/path/to/shell -c <scp command>

I think I can even update ContainerShell to leverage that, and run scp inside the container. This would be really nice because the location of /srdata over SSH will be the same as SCP.

While I was digging around, I think I could even support WinSCP using SCP. WinSCP works just like scp when doing sftp, which is the default protocol (it just evokes the shell with the arg for sftp-server). However, to do SCP, WinSCP has this wonky protocol where it sends stuff to stdin and waits. The stuff looks like basic shell commands, so I can probably just read stdin, execute those commands inside the container, then barf the output back to WinSCP over stdout. If not, I could at least detect something is wrong send a message to the user, then tear everything down.

[willnx]

I've figured out the source of this problem, it was in dockerpty. I forked and updated the code, and offered my changes back to them:
d11wtq/dockerpty#82

After spending a few days looking at the code, I'm just going to pull it into ContainerShell; no idea if they'll accept my changes, and it's been awhile since any PRs have been accepted.