bug#25581: 25.1; Incorrect statement in (elisp) `Hooks'

[Drew Adams]

>   >   Some vars are _intended_ to
>   > have a value that can be a single function or a list of
>   > functions.  Some of the latter kind of variables are
>   > hooks.  (Maybe _all_ of the latter can be treated as
>   > hooks; maybe not.)
> 
> We could conceivably start a long, slow process of giving them
> new names, and converting them into enitrely regular normal hooks.

Yes.  And then (or even before then), we should
update the doc to say that in the past _______ was
allowed.  This, to point out that there can be code
out there in the wild that still expects that.