Fix rmail-next/prev-same-subject.

 lisp/mail/rmail.el (rmail-simplified-subject): Decode subject with
 rfc2047-decode-string.
 (rmail-mime-toggle-hidden): Declare to avoid byte-compilation
 warnings.

lisp/ChangeLog

 2011-11-04  Eli Zaretskii  <eliz@gnu.org>
 
+	* mail/rmail.el (rmail-simplified-subject): Decode subject with
+	rfc2047-decode-string.
+	(rmail-mime-toggle-hidden): Declare to avoid byte-compilation
+	warnings.
+
 	* window.el (window-body-height, window-body-width): Mention in
 	the doc string that the return values are in frame's canonical
 	units.  (Bug#9949)

lisp/mail/rmail.el

@@ -194,6 +194,7 @@ please report it with \\[report-emacs-bug].")
 
 (declare-function mail-dont-reply-to "mail-utils" (destinations))
 (declare-function rmail-update-summary "rmailsum" (&rest ignore))
+(declare-function rmail-mime-toggle-hidden "rmailmm" ())
 
 (defun rmail-probe (prog)
   "Determine what flavor of movemail PROG is.
@@ -3262,6 +3263,7 @@ Interactively, empty argument means use same regexp used last time."
 Simplifying the subject means stripping leading and trailing whitespace,
 and typical reply prefixes such as Re:."
   (let ((subject (or (rmail-get-header "Subject" msgnum) "")))
+    (setq subject (rfc2047-decode-string subject))
     (if (string-match "\\`[ \t]+" subject)
 	(setq subject (substring subject (match-end 0))))
     (if (string-match rmail-reply-regexp subject)