bug#67171: 30.0.50; (At least) some VC commands fail with project-prefix-or-any-command

[Juri Linkov]

>> +(defcustom vc-deduce-backend-nonvc-modes
>> +  ;; Maybe we could even use comint-mode rather than shell-mode?
>>    '(dired-mode shell-mode eshell-mode compilation-mode)
>>    "List of modes not supported by VC where backend should be deduced.
>>  In these modes the backend is deduced based on `default-directory'.
>> -When nil, the backend is deduced in all modes.")
>> +When t, the backend is deduced in all modes."
>
> Please don't use "when" in these contexts; use "if" instead.  "When"
> could be confusing because it has the meaning of time, not only of
> condition.
>
> Also, it is better to say "If the value is t" or "If this is t",
> instead of just "If t".

Now changed to defcustom with these fixes.