Completely remove stringp check in special-display-p.

* window.el (special-display-p): Completely remove stringp
check.  Suggested by Andreas Schwab <schwab@linux-m68k.org>.

lisp/ChangeLog

+2012-06-18  Martin Rudalics  <rudalics@gmx.at>
+
+	* window.el (special-display-p): Completely remove stringp
+	check.  Suggested by Andreas Schwab <schwab@linux-m68k.org>.
+
 2012-06-17  Michael Albinus  <michael.albinus@gmx.de>
 
 	* minibuffer.el (read-file-name-default): Bind `non-essential' to `t'.

lisp/window.el

@@ -4192,8 +4192,6 @@ or matches BUFFER-NAME, the return value is the cdr of that
 entry."
   (let (tmp)
     (cond
-     ((not (stringp buffer-name))
-      (error "Invalid buffer name %s" buffer-name))
      ((member buffer-name special-display-buffer-names)
       t)
      ((setq tmp (assoc buffer-name special-display-buffer-names))