* gnus-art.el (gnus-article-mime-edit-exit): Bind
`mime-edit-insert-user-agent-field' to nil while `mime-edit-exit' is being
done; turn off font-lock first; query if the buffer is modified.
(gnus-article-mime-edit-done): New function.
(gnus-article-mime-edit-article-setup): Make the window fill its frame; clear
the buffere modified flag; substitute key definition `gnus-article-edit-done'
with `gnus-article-mime-edit-done'; don't turn off font-lock here; bind
`mime-edit-insert-user-agent-field' to nil while `mime-edit-exit' is being
done.
(gnus-article-mime-edit-article-unwind): Turn off font-lock first.