I've now designed two approaches to handle this.  The user interface is
the same: Move to some `change-log-list' item and type C-c C-t.  The
corresponding part of the source should be displayed in another window.


The simple approach is based on searching and comparing the result with
that of `add-log-current-defun'.  It works pretty well most of the time
but may exhibit the nasty behavior described in

http://lists.gnu.org/archive/html/emacs-devel/2007-10/msg00443.html

On my 1 GHz machine this means that I have to wait some 40 secs until
I'm told that there are no matches.  I can think of two ways to handle
this: (1) Convince Alan that the behavior of `c-beginning-of-defun' is
intolerable - AFAICT this has been tried before.  (2) Fix this within
`add-log-current-defun' to not use `c-beginning-of-defun' - I'm unable
to do this myself because I completely fail to understand that part of
the function.

I've attached the simple approach as add-log-simple.patch.


The more complicated approach is based on a combination of imenu, etags,
and regexp searching.  I've put most of this in a separate file called
local-tags.el merely because it would allow me to fix `which-func-mode'
and `imenu' as well (both are currently not really useful for c-mode).
This approach is more reliable and works faster for c-mode files.  It
requires, however, to have etags installed and working in order to get
reasonable behavior for c-mode change logs.

The second approach is attached as add-log-tags.patch and local-tags.el.
Note that add-log.el has (require 'local-tags) here, hence you have to
make sure that the latter is found.