Workhorse citing function which performs the initial citation.
This is callable from the various mail and news readers' reply
function according to the agreed upon standard. See the associated
info node `(SC)Top' for more details.
`sc-cite-original' does not do any yanking of the
original message but it does require a few things:
1) The reply buffer is the current buffer.
2) The original message has been yanked and inserted into the
reply buffer.
3) Verbose mail headers from the original message have been
inserted into the reply buffer directly before the text of the
original message.
4) Point is at the beginning of the verbose headers.
5) Mark is at the end of the body of text to be cited.
The region need not be active (and typically isn't when this
function is called). Also, the hook `sc-pre-hook' is run before,
and `sc-post-hook' is run after the guts of this function.
(fn)