Require `skeleton'.
(sml-mode): Add the menu for XEmacs. Make sure @ is a valid skeleton.
(sml-comment-indent): Remove.
(sml-mode-variables): Don't set comment-indent-function.
(sml-def-skeleton): Nop if skeletons aren't available.
(skeletons): Use `> _' and `@'.
(sml-forms-menu): Don't bother with easy-menu-filter-return crap.
(sml-cm-mode-syntax-table, sml-cm-font-lock-keywords): New vars.
(sml-cm-mode): Use define-derived-mode rather than define-generic-mode.
(sml-lex-font-lock-keywords, sml-lex-font-lock-defaults): New vars.
(sml-yacc-font-lock-keywords): Use sml-lex-font-lock-keywords.
Refine pattern to recognize the %prec keyword.
(sml-yacc-font-lock-defaults): Fix typo.