improve rmail's MIME handling

[Kenichi Handa <handa@m17n.org>]

A while ago, I reported that I need various settings to make
rmail handle MIME better (i.e. subject decoding/encoding),
and showed my settings including some additional functions,
but it seems that no one is working on this field.  So, I
started to work on it.  The attached is the first (and easy)
patch for summary lines.  Nowadays, not handling MIME
properly is regarded as a bug, and thus I want to install it
for Emacs 23.  What do you think?

---
Kenichi Handa
handa@m17n.org


2010-11-11  Kenichi Handa  <handa@m17n.org>

	* mail/rmailsum.el (rmail-header-summary): Handle multiline
	Subject: field.
	(rmail-summary-line-decoder): Set the default to
	rfc2047-decode-string.

=== modified file 'lisp/mail/rmailsum.el'
--- lisp/mail/rmailsum.el	2010-08-29 16:17:13 +0000
+++ lisp/mail/rmailsum.el	2010-11-11 02:33:42 +0000
@@ -364,12 +364,15 @@
       (aset rmail-summary-vector (1- msgnum) line))
     line))
 
-(defcustom rmail-summary-line-decoder (function identity)
+(require 'rfc2047)
+
+(defcustom rmail-summary-line-decoder (function rfc2047-decode-string)
   "Function to decode a Rmail summary line.
 It receives the summary line for one message as a string
 and should return the decoded string.
 
-By default, it is `identity', which returns the string unaltered."
+By default, it is `rfc2047-decode-string', which decodes MIME-encoded
+subject."
   :type 'function
   :group 'rmail-summary)
 
@@ -589,10 +592,17 @@
 						     (t (- mch 14))))
 				      (min len (+ lo 25)))))))))
    (concat (if (re-search-forward "^Subject:" nil t)
-	       (progn (skip-chars-forward " \t")
-		      (buffer-substring (point)
-					(progn (end-of-line)
-					       (point))))
+	       (let (pos str)
+		 (skip-chars-forward " \t")
+		 (setq pos (point))
+		 (forward-line 1)
+		 (setq str (buffer-substring pos (1- (point))))
+		 (while (looking-at "\\s ")
+		   (setq str (concat str " " 
+				     (buffer-substring (match-end 0)
+						       (line-end-position))))
+		   (forward-line 1))
+		 str)
 	     (re-search-forward "[\n][\n]+" nil t)
 	     (buffer-substring (point) (progn (end-of-line) (point))))
 	   "\n")))