Fix mail-default-headers handling in Message mode.

* gnus/message.el (message-default-mail-headers):
(message-default-headers): Carry the value mail-default-headers over
into message-default-mail-headers, rather than message-default-headers.

lisp/gnus/ChangeLog

+2010-03-27  Chong Yidong  <cyd@stupidchicken.com>
+
+	* message.el (message-default-mail-headers):
+	(message-default-headers): Carry the value mail-default-headers over
+	into message-default-mail-headers, rather than message-default-headers.
+
 2010-03-22  Juanma Barranquero  <lekktu@gmail.com>
 
 	* message.el (message-interactive): Doc fix.

lisp/gnus/message.el

@@ -1170,11 +1170,7 @@ It is a vector of the following headers:
   :valid-regexp "^\\'"
   :error "All header lines must be newline terminated")
 
-(defcustom message-default-headers
-  ;; Default to the value of `mail-default-headers' if available.
-  ;; Note: as for Emacs 21, XEmacs 21.4 and 21.5, it is unavailable
-  ;; unless sendmail.el is loaded.
-  (if (boundp 'mail-default-headers) mail-default-headers "")
+(defcustom message-default-headers ""
   "*A string containing header lines to be inserted in outgoing messages.
 It is inserted before you edit the message, so you can edit or delete
 these lines."
@@ -1187,16 +1183,18 @@ these lines."
   ;; Ease the transition from mail-mode to message-mode.  See bugs#4431, 5555.
   (concat (if (and (boundp 'mail-default-reply-to)
 		   (stringp mail-default-reply-to))
-	      (format "Reply-to: %s\n" mail-default-reply-to)
-	    "")
+	      (format "Reply-to: %s\n" mail-default-reply-to))
 	  (if (and (boundp 'mail-self-blind)
 		   mail-self-blind)
-	      (format "BCC: %s\n" user-mail-address)
-	    "")
+	      (format "BCC: %s\n" user-mail-address))
 	  (if (and (boundp 'mail-archive-file-name)
 		   (stringp mail-archive-file-name))
-	      (format "FCC: %s\n" mail-archive-file-name)
-	    ""))
+	      (format "FCC: %s\n" mail-archive-file-name))
+	  ;; Use the value of `mail-default-headers' if available.
+	  ;; Note: as for Emacs 21, XEmacs 21.4 and 21.5, it is
+	  ;; unavailable unless sendmail.el is loaded.
+	  (if (boundp 'mail-default-headers)
+	      mail-default-headers))
   "*A string of header lines to be inserted in outgoing mails."
   :version "23.2"
   :group 'message-headers