Add a testcase for closing display before exit

It works right now, lets keep it that way.

testsuite/gtk/Makefile.am

@@ -54,6 +54,7 @@ TEST_PROGS += 			\
 	treepath		\
 	treeview		\
 	window			\
+	displayclose		\
 	$(NULL)
 
 if OS_UNIX

testsuite/gtk/displayclose.c

+#include <gtk/gtk.h>
+
+int
+main (int argc, char **argv)
+{
+  const gchar *display_name;
+  GdkDisplay *display;
+  GtkWidget *win, *but;
+
+  g_log_set_always_fatal (G_LOG_LEVEL_WARNING | G_LOG_LEVEL_CRITICAL);
+
+  if (!gtk_parse_args (&argc, &argv))
+    return 1;
+
+  display_name = gdk_get_display_arg_name();
+  display = gdk_display_open(display_name);
+
+  if (!display)
+    return 1;
+
+  gdk_display_manager_set_default_display (gdk_display_manager_get (), display);
+
+  win = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+  g_signal_connect (win, "destroy",
+		    G_CALLBACK (gtk_main_quit), NULL);
+  g_signal_connect (win, "delete-event",
+                    G_CALLBACK (gtk_widget_destroy), NULL);
+
+  but = gtk_button_new_with_label ("Try to Exit");
+  g_signal_connect_swapped (but, "clicked",
+			    G_CALLBACK (gtk_widget_destroy), win);
+  gtk_container_add (GTK_CONTAINER (win), but);
+
+  gtk_widget_show_all (win);
+
+  gtk_test_widget_wait_for_draw (win);
+
+  gdk_display_close (display);
+
+  return 0;
+}