Reminder: Add ssh_config equivalents of -N, -n and -f

[Volker Diels-Grabsch]

Hi Damien,

Damien Miller wrote:
> I think SessionType=none/subsystem/default is the way to go. I'll
> have some time to look at it next week, but if you want to implement
> it then please don't let me stop you :)

Okay, finished:

    https://github.com/openssh/openssh-portable/pull/231

I also replaced the internal 2 flags with a single option enum (integer).


Please note one subtle consequence here:

Combining the flags in a single value means that it is no longer
possible to have the "no_shell_flag" (-N) and "subsystem_flag" (-s)
enabled at the same time.  This is good in itself, and among others,
this means that edge cases, where both "-N" and "-s" are given to ssh,
are now handled in a more logical way: The last provided one wins.

Is that okay?

Or, do we needed backwards-compatibility-by-all-means here?

    (Which would mean in this case: "-N" always takes precedence over "-s".)


Best regards,
Volker

-- 
Volker Diels-Grabsch
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