Avoid infinite loop when replacing escapes

Patch by David Maus, who writes:

> Org enters an infinite loop when `org-replace-escapes' is called with
> a table containing a replace string that contains the escape sequence
> it should be replaced with.
>
> Example:
> ,----
> | (org-replace-escapes "%m" '(("%m" . "87zl0qq1f3.wl%maus.david@gmail.com")))
> `----
>
> I stumpled upon when I tried to store a link to a internet message
> whose message id contained the sequence "%m" (perfectly valid for a
> message id) while using "%m" as message description.
>
> Attached patch fixes this by
>
>  1. detecting such 'self reference' and replacing the offending
>     sequence in the replace string by a string with a text property
>     that contains the original sequence
>
>  2. replacing occurences of substrings with this text property by the
>     original sequence.

lisp/ChangeLog

@@ -1,3 +1,8 @@
+2010-05-08  David Maus  <dmaus@ictsoc.de>
+
+	* org.el (org-replace-escapes): Avoid infinite loop when
+	replace string contains escape sequence it replaces.
+
 2010-05-08  Carsten Dominik  <carsten.dominik@gmail.com>
 
 	* org-crypt.el (org-crypt-key-for-heading): Use symmetric

lisp/org.el

@@ -17644,17 +17644,27 @@ TABLE is an association list with keys like \"%a\" and string values.
 The sequences in STRING may contain normal field width and padding information,
 for example \"%-5s\".  Replacements happen in the sequence given by TABLE,
 so values can contain further %-escapes if they are define later in TABLE."
-  (let ((case-fold-search nil)
-	e re rpl)
-    (while (setq e (pop table))
+  (let ((tbl (copy-alist table))
+	(case-fold-search nil)
+        (pchg 0)
+        e re rpl)
+    (while (setq e (pop tbl))
       (setq re (concat "%-?[0-9.]*" (substring (car e) 1)))
+      (when (string-match re (cdr e))
+        (let ((sref (substring (cdr e) (match-beginning 0) (match-end 0)))
+              (safe "SREF"))
+          (add-text-properties 0 3 (list 'sref sref) safe)
+          (setcdr e (replace-match safe t t (cdr e)))))
       (while (string-match re string)
-	(setq rpl (format (concat (substring (match-string 0 string) 0 -1) "s")
-			  (cdr e)))
-	(setq string (replace-match rpl t t string))))
+        (setq rpl (format (concat (substring (match-string 0 string) 0 -1) "s")
+                          (cdr e)))
+        (setq string (replace-match rpl t t string))))
+    (while (setq pchg (next-property-change pchg string))
+      (let ((sref (get-text-property pchg 'sref string)))
+	(when (and sref (string-match "SREF" string pchg))
+	  (setq string (replace-match sref t t string)))))
     string))
 
-
 (defun org-sublist (list start end)
   "Return a section of LIST, from START to END.
 Counting starts at 1."