Improve the custom type of some user options.

Improve the custom type of some user options.

* lisp/autoinsert.el (auto-insert-alist):
* lisp/replace.el (query-replace-from-to-separator):
* lisp/gnus/gnus-art.el (gnus-hidden-properties):
* lisp/gnus/gnus-gravatar.el (gnus-gravatar-properties):
* lisp/gnus/gnus-picon.el (gnus-picon-properties):
* lisp/progmodes/prolog.el (prolog-keywords, prolog-types)
(prolog-mode-specificators, prolog-determinism-specificators)
(prolog-directives, prolog-program-name, prolog-program-switches)
(prolog-consult-string, prolog-compile-string, prolog-eof-string)
(prolog-prompt-regexp): Improve custom type.