ox-icalendar: Use \r\n instead of \n as line breaks

* lisp/ox-icalendar.el (org-icalendar-fold-string): Break lines with
  \r\n instead of \n, per RFC 5545.

Reported-by: Stephen Eglen <sje30@cam.ac.uk>
<http://permalink.gmane.org/gmane.emacs.orgmode/110306>

lisp/ox-icalendar.el

@@ -458,7 +458,7 @@ or subject for the event."
    (mapconcat
     (lambda (line)
       ;; Limit each line to a maximum of 75 characters.  If it is
-      ;; longer, fold it by using "\n " as a continuation marker.
+      ;; longer, fold it by using "\r\n " as a continuation marker.
       (let ((len (length line)))
 	(if (<= len 75) line
 	  (let ((folded-line (substring line 0 75))
@@ -468,11 +468,11 @@ or subject for the event."
 	    ;; line, real contents must be split at 74 chars.
 	    (while (< (setq chunk-end (+ chunk-start 74)) len)
 	      (setq folded-line
-		    (concat folded-line "\n "
+		    (concat folded-line "\r\n "
 			    (substring line chunk-start chunk-end))
 		    chunk-start chunk-end))
-	    (concat folded-line "\n " (substring line chunk-start))))))
-    (org-split-string s "\n") "\n")))
+	    (concat folded-line "\r\n " (substring line chunk-start))))))
+    (org-split-string s "\n") "\r\n")))