bug#9993: `vc-svn-checkin' needs "--non-interactive"

[Stefan Monnier]

>>> or make vc-svn-command unconditionally add it
>> That sounds right.
> Done.
>> We can add a comment in our code that --non-interactive is a workaround
>> and that svn should do it automatically since we're using a pipe.
> Gotta cater to the common use case of
>   find . -name '*.pdf' | xargs svn update

Yes, I think the real test is not "is stdin a tty" but "are we connected
to a tty", which would work right in both cases (an Emacs subprocess
connected via a pipe does not have an associated tty whereas the above
svn command would if typed in bash).


        Stefan