Avoid any possibilty of prompting in ssh setup in webapp.
Prticularly on Windows this was a problem, it seemed to enter an infinite
loop. I think that ssh can sometimes use SSH_ASKPASS for y/n prompting,
when no controlling TTY is available, and since git-annex always answers
back with the host's password, not y/n, it looped.
This commit was sponsored by Simon Michael.
When setting up a remote on a ssh server, prompt for a password inside the
webapp, rather than relying on ssh's own password prompting in the terminal
the webapp was started from, or ssh-askpass.
Avoids double prompting for the ssh password (and triple-prompting on
windows for rsync.net), since the entered password is cached for 10 minutes
and this cached password is reused when setting up the repository, after
the initial probe.
When the user has an existing ssh key set up, they can choose to use it,
rather than entering a password. The webapp used to probe for this case
automatically, so this is a little harder, but it's an advanced user thing.
Note that this commit is known to break enabling existing rsync
repositories. It hs not been tested with gcrypt repositories. It's not been
successfully tested yet on Windows.
This commit was sponsored by Ralph Mayer.
This avoids ssh prompting for passwords on stdin, ever.
It may also change other behavior of other programs, as there is no
controlling terminal now. However, setsid was already done when running the
assistant in daemon mode, so any behavior changes should not be really new.
