Setting the page flow

Here is the area where GtkAssistant and GnomeDruid differ the most. While GnomeDruid used the "next" and "back" signals from the GnomeDruidPage, GtkAssistant uses the following techniques:

A sample GtkAssistantPageFunc could look like this:

static gint
forward_page_function (gint     current_page,
                       gpointer data)
  switch (current_page)
    case 0:
      return 1;
    case 1:
      if (check_page1_data ())
	   return 2;
	   return 3;
    case 2:
      return 3;
      return -1;