message.el patch

[Geoff Greene]

i just wrote a quick patch for lisp/gnus/message.el to fix an issue i have
with it.  it resets the filename of the buffer to *message* in your drafts
directory, even if the buffer already has an associate file.

this patch fixes it so that the filename will only be reset if the buffer
is not already associated with a file.  this way you can edit an email on
disk, rather than sending it, posting it to usenet, or whatever.  this is
good for people who use newsreaders like tin that start up $EDITOR to
compose messages, and want to write them using message-mode.

i'm only just teaching myself elisp, so i might not have done it the best
way, but it seems to work for me.

message.el.diff
Description: Text document