(ada-mode): Avoid unneeded version checks.

(ada-mode): Avoid unneeded version checks.
Don't change compile-auto-highlight globally.
Don't bother with `font-lock-defaults' property since XEmacs
also understands the `font-lock-defaults' variable.
Use make-local-variable rather than make-variable-buffer-local.
Don't `defconst' comment-indent-function: keep the default.
Call easy-menu-add unconditionally.
(ada-create-keymap): Use [(shift tab)] so it works on both Emacsen.
(ada-create-menu): Use :included for Emacs as well.