bug#1741: 23.0.60; vc fail to register file while logged as /su:: with tramp

[Stefan Monnier]

>> As explained, I'd just start with the simplest possible solution because
>> I expect it will be sufficient.
> Committed. Let's see, whether people complain.

BTW, to improve the behavior in case of things like "git status", it
might be worthwhile to add some way to indicate that a particular use of
process-file is (supposed to be) free of side-effects.


        Stefan