Mail mode and message mode hooks

[Chong Yidong <cyd@stupidchicken.com>]

I'd like to hear some opinions on how to treat the mail mode and message
mode hooks, given that message-mode is to be the default.

As it stands, anyone using feedmail will likely suffer breakage in
upgrading to Emacs 23.2, as shown in bug#3942.  The feedmail package
relies on hooks, and contains documentation like this:

   feedmail-mail-send-hook-splitter is a Lisp function in `feedmail.el'.

   (feedmail-mail-send-hook-splitter)

   Facilitate dividing `mail-send-hook' things into queued and immediate
   cases.  If you have `mail-send-hook' functions that should only be
   called for sending/ queueing messages or only be called for the
   sending of queued messages, this is for you.  Add this function to
   `mail-send-hook' with something like this:

       (add-hook 'mail-send-hook 'feedmail-mail-send-hook-splitter)

So, the message-*-hook variables should probably be aliased to the
mail-*-hook variables.

One problem that I can see with this is that code intended for one mode
may not work properly for the other mode, but I can't think of any
concrete examples.  Any thoughts?