* nndraft.el (nndraft-generate-headers): New function.

* nndraft.el (nndraft-generate-headers): New function.
(nndraft-request-associate-buffer): Use it to write headers on
buffer save.

* message.el (message-generate-headers): Let the function be a
lambda form.
(message-draft-headers): New variable.

* gnus-msg.el (gnus-inews-make-draft-meta-information): New
function.
(gnus-setup-message): Use it.

* message.el (message-generate-headers-first): Doc fix.
(message-setup-1): Use new function for getting which headers to
generate.
(message-headers-to-generate): New function.