Avoid display corruption on :vsp and 'go' changes

Always redraw the screen when splitting vertically or when the 'go'
option is modified (it may e.g. cause scrollbars to hide/show).

src/option.c

@@ -1277,7 +1277,13 @@ static struct vimoption
 			    (char_u *)NULL, PV_NONE,
 #endif
 			    {(char_u *)50L, (char_u *)0L} SCRIPTID_INIT},
-    {"guioptions",  "go",   P_STRING|P_VI_DEF|P_RALL|P_FLAGLIST,
+    {"guioptions",  "go",   P_STRING|P_VI_DEF|P_RALL|P_FLAGLIST
+# ifdef FEAT_GUI_MACVIM
+	/* Scrollbars etc. may change the view, if this happens without a
+	 * redraw the display may get corrupted, so always redraw. */
+			    |P_RCLR
+# endif
+			    ,
 #if defined(FEAT_GUI)
 			    (char_u *)&p_go, PV_NONE,
 # if defined(UNIX) && !defined(MACOS)

src/window.c

@@ -1097,7 +1097,12 @@ win_split_ins(size, flags, newwin, dir)
      */
     redraw_win_later(wp, NOT_VALID);
     wp->w_redr_status = TRUE;
+#ifdef FEAT_GUI_MACVIM
+    /* The view may have moved, so clear all or display may get corrupted. */
+    redraw_win_later(oldwin, CLEAR);
+#else
     redraw_win_later(oldwin, NOT_VALID);
+#endif
     oldwin->w_redr_status = TRUE;
 
     if (need_status)
@@ -5575,7 +5580,12 @@ win_new_width(wp, width)
 	update_topline();
 	curs_columns(TRUE);	/* validate w_wrow */
     }
+#ifdef FEAT_GUI_MACVIM
+    /* The view may have moved, so clear all or display may get corrupted. */
+    redraw_win_later(wp, CLEAR);
+#else
     redraw_win_later(wp, NOT_VALID);
+#endif
     wp->w_redr_status = TRUE;
 }
 #endif