RE: dropped 4th arg from all-completions

[Drew Adams]

> > Emacs does not raise an error, but it does not respect the arg.
> 
> (all-completions "" '(" asdfgh") nil nil)
>    => (" asdf")
>
> (all-completions "" '(" asdfgh") nil t)
>    => nil

Mille excuses for that part. I apparently checked only with a string that starts
with a space, which is the exceptional case where matching occurs anyway
("ignored unless STRING itself starts with a space"):

(all-completions " abc" '((" abc") ("a")) nil t)
=> (" abc")

That doesn't change the rest, but I'm glad this is still supported under the
covers.

The 4th arg should not be deprecated and it should be documented normally. And
changes like this should not be made with no proposal, no reasons given (still
the case), and no discussion.