2.21.5 (unstable):

* Adapt to recent GDK and Gtk+ deprecations.
  You may need to include gtkmm/box, gtkmm/dialog.h, gtkmm/main.h,
  gtkmm/treepath, or gtkmm.h before other gtkmm or gtk+ includes to build with
  disabled deprecations and warnings as errors.
  We might yet find a way to make that unnecessary. It is only an issue in
  gtkmm 2.22, not with gtkmm-3.0.
  (Murray Cumming)
* PrintOperation: get_default_page_setup(): refcount fix.
  (Murray Cumming) Bug #622957 (Kjell Ahlstedt).