title: Gtk Notebook "change-current-page" doesn't work
body: <p>i am using gtk notebook. I need to if user change current page, some
  button should be active. But current-page-change doesn't work, so
  nothing happens. I tried "switch-page" signal but it gives me previous
  page number when i asked "notebook.page". But i need to if user change
  current page, i should know which page is selected.</p>