bug#19400: 24.4.50; `completion-separator-self-insert-command' calls `undefined' with error

[Drew Adams]

> > emacs -Q -f dynamic-completion-mode
> 
> > Instead of "^ is undefined", I get
> > "completion-separator-self-insert-command: Wrong number of
> > arguments: (0 . 0), 1"

FWIW, I don't see that problem at all, with this build (the latest
one I have):

In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
 of 2014-11-30 on LEG570
Repository revision: 3517da701ea5d16c296745d6678988b06bee615d
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --without-dbus --enable-checking=yes,glyphs
 CPPFLAGS=-DGLYPH_DEBUG=1'

With emacs -Q -f dynamic-completion-mode I just get that mode turned on in 
*scratch*, and dynamic completion works fine.  And I see no such problem with 
official releases through Emacs 24.4 either.

> Does the patch below fix this problem (I'm pretty sure it does), and
> more importantly, does it seem to preserve the expected behavior?

I haven't tried it. But why rewrite so much, just to fix this problem (if it is 
indeed a problem and a fix)?

If this is a regression introduced sometime after the build I mentioned above, 
then why not concentrate on the code change that led to the breakage? It surely 
wasn't a change in the completions.el code that introduced a regression here.

FWIW, just looking at the patch I wonder what happened to the autofill behavior 
of SPC...