Remove the post_main() mechanism.

This existed in order to avoid the various confusions that could
happen if a toplevel callback ran in the context of a subsidiary
instance of gtk_main(). Now there aren't any subsidiary gtk_main
instances any more, this mechanism is no longer needed, and I can
throw it out. It was horrible anyway.

unix/gtkcomm.c

@@ -203,40 +203,9 @@ static int idle_fn_scheduled;
 
 static void notify_toplevel_callback(void *);
 
-/*
- * Replacement code for the gtk_quit_add() function, which GTK2 - in
- * their unbounded wisdom - deprecated without providing any usable
- * replacement, and which we were using to ensure that our idle
- * function for toplevel callbacks was only run from the outermost
- * gtk_main().
- *
- * We must make sure that all our subsidiary calls to gtk_main() are
- * followed by a call to post_main(), so that the idle function can be
- * re-established when we end up back at the top level.
- */
-void post_main(void)
-{
-    if (gtk_main_level() == 1)
-        notify_toplevel_callback(NULL);
-}
-
 static gint idle_toplevel_callback_func(gpointer data)
 {
-    if (gtk_main_level() > 1) {
+    run_toplevel_callbacks();
-        /*
-         * We don't run callbacks if we're in the middle of a
-         * subsidiary gtk_main. So unschedule this idle function; it
-         * will be rescheduled by post_main() when we come back up a
-         * level, which is the earliest we might actually do
-         * something.
-         */
-        if (idle_fn_scheduled) {      /* double-check, just in case */
-            g_source_remove(toplevel_callback_idle_id);
-            idle_fn_scheduled = FALSE;
-        }
-    } else {
-        run_toplevel_callbacks();
-    }
 
     /*
      * If we've emptied our toplevel callback queue, unschedule

unix/unix.h

@@ -161,7 +161,6 @@ enum DialogSlot {
 void register_dialog(void *frontend, enum DialogSlot slot, GtkWidget *dialog);
 void unregister_dialog(void *frontend, enum DialogSlot slot);
 #endif
-void post_main(void);     /* called after any subsidiary gtk_main() */
 
 /* Things pterm.c needs from gtkdlg.c */
 #ifdef MAY_REFER_TO_GTK_IN_HEADERS