Putty does not exit when remote command terminates

[Antoine Martin]

In ssh-mode, we launch a remote X command and putty is still running when the command terminates.
This causes the session to remain "active" on the client despite the fact that it is really finished...

Attempts at using TortoisePlink?.exe, changing subprocess.Popen pipe options, etc.. have all failed. Need to start again with a fresh test case (Xming + plink + hardcoded command for testing).