* lisp/progmodes/prolog.el: Use SMIE. Cleanup regexp setup.

* lisp/progmodes/prolog.el: Use SMIE.  Cleanup regexp setup.
(prolog-upper-case-string, prolog-lower-case-string)
(prolog-atom-char-regexp, prolog-atom-regexp): Initialize in defconst.
(prolog-use-smie, prolog-smie-grammar): New vars.
(prolog-smie-forward-token, prolog-smie-backward-token)
(prolog-smie-rules): New funs.
(prolog-comment-indent): Remove.
(prolog-mode-variables): Use default comment indentation instead.
Setup SMIE.
(prolog-build-case-strings, prolog-set-atom-regexps): Remove.
(prolog-mode): Don't call them any more.
(prolog-electric-colon, prolog-electric-dash)
(prolog-edit-menu-insert-move): Use indent-according-to-mode.