bug#553: 23.0.60; Unknown button type `quail-keyboard-layout-button'

[Chong Yidong]

> > Do you remember why you wrote quail-help-init this way?  It seems
> > unnecessary; why not define the button types directly at the top level
> > of quail.el?
>
> I don't know the reason of writing quail-help-init this way, but it seems
> it was to not load `help-mode' after loading `quail.el'.  `help-mode' is
> not necessary for quail's operations, so its loading should be postponed
> for rare cases when the user needs to see the help buffer with keyboard
> layouts.

Right, but why do we have to put the button definitions inside
quail-help-init?  In other words, why not the following?

*** trunk/lisp/international/quail.el.~1.164.~  2008-05-06 00:18:15.000000000 
-0400
--- trunk/lisp/international/quail.el   2008-08-26 17:09:39.000000000 -0400
***************
*** 2424,2450 ****
        (insert ?\n))
        (insert ?\n))))
  
! (defun quail-help-init ()
!   (unless (featurep 'help-mode)
!     (require 'help-mode)
!     (define-button-type 'quail-keyboard-layout-button
!       :supertype 'help-xref
!       'help-function '(lambda (layout)
!                       (help-setup-xref `(quail-keyboard-layout-button ,layout)
!                                        nil)
!                       (quail-show-keyboard-layout layout))
!       'help-echo (purecopy "mouse-2, RET: show keyboard layout"))
! 
!     (define-button-type 'quail-keyboard-customize-button
!       :supertype 'help-customize-variable
!       'help-echo (purecopy "mouse-2, RET: customize keyboard layout"))))
  
  (defun quail-help (&optional package)
    "Show brief description of the current Quail package.
  Optional arg PACKAGE specifies the name of alternative Quail
  package to describe."
    (interactive)
!   (quail-help-init)
    (let ((help-xref-mule-regexp help-xref-mule-regexp-template)
        (mb enable-multibyte-characters)
        (package-def
--- 2424,2447 ----
        (insert ?\n))
        (insert ?\n))))
  
! (define-button-type 'quail-keyboard-layout-button
!   :supertype 'help-xref
!   'help-function '(lambda (layout)
!                   (help-setup-xref `(quail-keyboard-layout-button ,layout)
!                                    nil)
!                   (quail-show-keyboard-layout layout))
!   'help-echo (purecopy "mouse-2, RET: show keyboard layout"))
! 
! (define-button-type 'quail-keyboard-customize-button
!   :supertype 'help-customize-variable
!   'help-echo (purecopy "mouse-2, RET: customize keyboard layout"))
  
  (defun quail-help (&optional package)
    "Show brief description of the current Quail package.
  Optional arg PACKAGE specifies the name of alternative Quail
  package to describe."
    (interactive)
!   (require 'help-mode)
    (let ((help-xref-mule-regexp help-xref-mule-regexp-template)
        (mb enable-multibyte-characters)
        (package-def