Improve keymap handling

[Ikumi Keita]

Hi all,

I'd propose to commit the attached patch. What do you think about it?

1. As `LaTeX-common-initialization' contains
  (define-key LaTeX-mode-map "\C-xne" #'LaTeX-narrow-to-environment)
, it re-binds C-x n e to `LaTeX-narrow-to-environment' every time emacs
opens LaTeX document. It doesn't hurt, but is a kind of waste.

Since `VirTeX-common-initialization' contains
  (define-key TeX-mode-map "\C-xng" #'TeX-narrow-to-group)
, similar argument applies for `TeX-narrow-to-group'.

I think it's enough to make those bindings just once when AUCTeX first
constructs (La)TeX-mode-map.

2. Similar argument applies for binding of preview button on tool bar.
Since `LaTeX-mode-hook' contains `preview-mode-setup', it binds tool bar
button to `preview-at-point' again and again.

3. Now that all supported emacsens have `beginning-of-defun-function'
and `end-of-defun-function', we can (should?) make use of them instead
of overwriting bindings of C-M-a and C-M-e explicitly in
`LaTeX-mode-map'.

Does anyone find difficulties about these ideas?

Regards,
Ikumi Keita

0001-Improve-keymap-handling.patch
Description: keymap patch