(TopLevel): Use `static-if', requiring "static" at the compile time.

(TopLevel): Use `static-if', requiring "static" at the compile time.
(gnus-offline-hangup-function): Abolish.
(gnus-offline-auto-ppp): New variable.
(gnus-offline-gnus-get-new-news): Refer to it.
(gnus-offline-set-unplugged-state): Ditto.
(gnus-offline-set-auto-ppp): New function. It replaces the
function `gnus-offline-toggle-auto-hangup'.
(gnus-offline-toggle-auto-hangup): Abolish.
(gnus-offline-define-menu-and-key): Use `static-if' and
`static-cond'.
(gnus-offline-popup-menu): Do not define this function under XEmacs.
(gnus-offline-popup): New function.