(reb-mode-common): Remove reference to bogus variable `reb-kill-buffer';

(reb-mode-common): Remove reference to bogus variable `reb-kill-buffer';
don't make hooks buffer-local, use the LOCAL arg of `add-hook'.
(reb-blink-delay, reb-mode-hook, reb-re-syntax, reb-auto-match-limit):
Remove spurious * from defcustom docstrings.
(reb-next-match, reb-prev-match, reb-enter-subexp-mode): Fix typos in messages.
(reb-mode-buffer-p): New function.
(re-builder, reb-kill-buffer): Use `reb-mode-buffer-p'.  Use `when'.
(top, reb-show-subexp, reb-auto-update, reb-auto-update, reb-delete-overlays,
reb-cook-regexp, reb-update-regexp, reb-update-overlays): Use `unless', `when'.
(re-builder-unload-function): New function.