* lisp/gnus: Use `declare`.

* lisp/gnus: Use `declare`.

* lisp/gnus/nnoo.el (defvoo, deffoo, nnoo-declare, nnoo-import)
(nnoo-map-functions):
* lisp/gnus/nnmaildir.el (nnmaildir--with-nntp-buffer)
(nnmaildir--with-work-buffer, nnmaildir--with-nov-buffer)
(nnmaildir--with-move-buffer, nnmaildir--condcase):
* lisp/gnus/mm-decode.el (mm-with-part):
* lisp/gnus/gnus-msg.el (gnus-setup-message):
* lisp/gnus/gnus-agent.el (gnus-agent-with-fetch, gnus-agent-while-plugged):
* lisp/gnus/mail-source.el (mail-source-set-1, mail-source-value):
Use `declare`.

* lisp/gnus/gnus-util.el (gnus-define-keys): Use `declare`, and also
don't quote `keymap` if it's a variable name.
(gnus-define-keys-1): Reject the case where `keymap` is a variable name.
(gnus-eval-in-buffer-window, gnus-define-keys-safe)
(gnus-define-keymap, gnus-atomic-progn, gnus-with-output-to-file)
(gnus-parse-without-error): Use `declare`.
(gnus-atomic-progn-assign, gnus-atomic-setq): Delete macros.

* lisp/gnus/gnus-undo.el (gnus-undo-register): Drop indent and edebug spec
since they're not really appropriate for a function.

* lisp/gnus/gnus-art.el (gnus--\,@): New macro.
Use it at top-level to construct the `gnus-article-FOO` => `article-FOO`
wrapper functions.
(gnus-with-article-headers, gnus-with-article-buffer): Use `declare`.