Ensure that rcirc-buffer-alist has no text properties

* rcirc.el (rcirc-mode): Remove text properties from
  rcirc-buffer-alist keys

lisp/net/rcirc.el

@@ -1317,8 +1317,9 @@ This number is independent of the number of lines in the buffer.")
   (when target				; skip server buffer
     (let ((buffer (current-buffer)))
       (with-rcirc-process-buffer process
-	(setq rcirc-buffer-alist (cons (cons target buffer)
-				       rcirc-buffer-alist))))
+        (push (cons (set-text-properties 0 (length target) nil target)
+                    buffer)
+              rcirc-buffer-alist)))
     (rcirc-update-short-buffer-names))
 
   (add-hook 'completion-at-point-functions