RE: `interactive-form` symbol property

[Drew Adams]

> > You can't advise a function that doesn't exist yet.
> Yes, you can.

True; forgot that.  Subtract one from the reasons not
to deprecate it. ;-)

> > (To be clear, I haven't used this property.
> > I have used the function of the same name, however.)
> 
> The function of the same name is "unrelated" in the sense that I am
> definitely not suggesting we obsolete the `interactive-form` function.

Understood.

On the other hand, if we changed `interactive' to always
set the property then that function would be redundant,
even if convenient for mapping, `funcall' etc.  And no,
I'm not suggesting we do that and then deprecate the
function. ;-)  I think both can be useful.