Fix horizontal scroll bar dragging in R2L paragraphs.

 src/w32term.c (w32_horizontal_scroll_bar_handle_click): Fix the
 second coordinate ('y') reported for dragging the horizontal
 scroll bar thumb.

src/ChangeLog

+2014-08-19  Eli Zaretskii  <eliz@gnu.org>
+
+	* w32term.c (w32_horizontal_scroll_bar_handle_click): Fix the
+	second coordinate ('y') reported for dragging the horizontal
+	scroll bar thumb.
+
 2014-08-19  YAMAMOTO Mitsuharu  <mituharu@math.s.chiba-u.ac.jp>
 
 	* xdisp.c (erase_phys_cursor): Fix confusion between window-relative

src/w32term.c

@@ -4310,7 +4310,10 @@ w32_horizontal_scroll_bar_handle_click (struct scroll_bar *bar, W32Msg *msg,
       case SB_THUMBTRACK:
       case SB_THUMBPOSITION:
 	if (HORIZONTAL_SCROLL_BAR_LEFT_RANGE (f, bar->width) <= 0xffff)
-          x = HIWORD (msg->msg.wParam);
+	  {
+	    x = HIWORD (msg->msg.wParam);
+	    y = si.nMax - x - si.nPage;
+	  }
 	bar->dragging = 1;
 	emacs_event->part = scroll_bar_horizontal_handle;