bug#5293: 23.1; unload-feature on buffer-local hooks

[Kevin Ryde]

When `unload-feature' looks in hooks for functions that it's going to
unload, it doesn't seem to look in buffer-local values, other than for
the current buffer.

Evalling the code in try-foo.el below loads then unloads foo.el.  It
gets an error

    void-function foo-message

where I hoped unload-feature might have purged that `foo-message' from
`after-change-functions'.

I suppose looking in all buffers is more work for unload-feature, but
would be a good protection against bad things happening later.  I expect
some of the standard hooks like `after-change-functions' are used
buffer-local most of the time.

If instead it's an intentional omission (to save work) then the elisp
manual and the docstring could note it so that modes or packages using
buffer-local hook settings can take steps to undo.

foo.el
Description: application/emacs-lisp

try-foo.el
Description: application/emacs-lisp

In GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.16.5)
 of 2009-09-14 on raven, modified by Debian
configured using `configure  '--build=i486-linux-gnu' '--host=i486-linux-gnu' 
'--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' 
'--localstatedir=/var/lib' '--infodir=/usr/share/info' 
'--mandir=/usr/share/man' '--with-pop=yes' 
'--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim'
 '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 
'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g 
-O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_AU
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-1-unix
  default-enable-multibyte-characters: t