bug#13581: 24.3.50; regression: defadvice does not work, to augment doc string

[Drew Adams]

I cannot download a pretest binary and try this in that now.  Could someone else
please try it?  If this is a regression also in the pretest (not just in the
trunk), then I think it should be fixed before the release.  Thx.

> emacs -Q
>  
> (defun frog () (interactive) (message "croak"))
> (define-key isearch-mode-map "\C-o" 'frog)
> (defadvice isearch-forward (before froggy activate)
>   "\\<isearch-mode-map>\\[frog] - hear Froggy croak")
>  
> C-h f isearch-forward
>  
> No Froggy to be seen.  Worked in previous Emacs versions, 
> including 24.2.
> 
>  
> In GNU Emacs 24.3.50.1 (i386-mingw-nt5.1.2600)
>  of 2013-01-25 on ODIEONE