Avoid warnings from cus-start.el regarding scroll-bar-adjust-thumb-portion.

 lisp/cus-start.el (all): Avoid warnings about
 scroll-bar-adjust-thumb-portion on platforms where it is not
 defined.

lisp/ChangeLog

+2013-01-13  Eli Zaretskii  <eliz@gnu.org>
+
+	* cus-start.el (all): Avoid warnings about
+	scroll-bar-adjust-thumb-portion on platforms where it is not
+	defined.
+
 2013-01-11  Jan Djärv  <jan.h.d@swipnet.se>
 	* cus-start.el (all): Add scroll-bar-adjust-thumb-portion.

lisp/cus-start.el

@@ -576,6 +576,9 @@ since it could result in memory overflow and make Emacs crash."
 			      (symbol-name symbol))
 		       ;; Any function from fontset.c will do.
 		       (fboundp 'new-fontset))
+		      ((equal "scroll-bar-adjust-thumb-portion"
+			      (symbol-name symbol))
+		       (featurep 'x))
 		      (t t))))
     (if (not (boundp symbol))
 	;; If variables are removed from C code, give an error here!