🚀 go-pugleaf

A user was surprised to find that the text-mode commands (in
particular m-s -- centRE-line) aren't available in mail-mode.

This is particularly confusing because mail-mode calls text-mode-hook
-- one would expect mail-mode to be `built' on text-mode

We fixed this by defining these commands in her mail-mode-hook.
I would think that a better solution would be to fix mail-mode-map's
initialisation to be:

(if mail-mode-map
    nil
  ;(setq mail-mode-map (make-sparse-keymap))
  (setq mail-mode-map (copy-keymap text-mode-map))
  (local-set-key mail-mode-map ...)
  ...)

Other modes which are `conceptually' text-modes (in particular, those
which call text-mode-hook) could be similarly fixed.

[This is far from the first time I've been screwed by the fact the
emacs has only local and global keymaps, rather than a hierarchy of
keymaps which inherit from each other...  Sigh.]