(mouse-split-window-vertically): Treat scroll bar events just like others.

lisp/mouse.el

@@ -89,10 +89,7 @@ This command must be bound to a mouse click."
   (mouse-minibuffer-check click)
   (let ((start (event-start click)))
     (select-window (posn-window start))
-    (let ((new-height (if (eq (posn-point start) 'vertical-scroll-bar)
-			  (scroll-bar-scale (posn-col-row start)
-					    (1- (window-height)))
-			(1+ (cdr (posn-col-row (event-end click))))))
+    (let ((new-height (1+ (cdr (posn-col-row (event-end click)))))
 	  (first-line window-min-height)
 	  (last-line (- (window-height) window-min-height)))
       (if (< last-line first-line)