bug#8613: "mode:" for minor-mode breaks set-visited-file-name

[Glenn Morris]

Stefan Monnier wrote:

>> The fact that "mode:" is allowed to indicate both major and minor modes
>> in file local variables is problematic. Things would be much simpler if
>> a different convention were used for minor modes.
>
> Agreed,

So; shall we try to come up with a new convention for enabling
minor-modes via file-local variables, and deprecate using mode: for that?

All "mode:" does is funcall FOO-mode [1], which is nothing that can't be
done with :eval, except the latter will prompt for confirmation. Rather
than adding eg "minor-mode:", maybe safe-local-eval-forms could be
extended with a regexp element matching something like "([a-z]+-mode)".

[1] Well, it also ignores unknown modes.