Gtk::Button: Deprecate the alignment API which is deprecated in GTK+
Gtk::Button: Deprecate the alignment API which is deprecated in GTK+

* gtk/src/button.hg: Deprecate set_alignment(), get_alignment(),
property_xalign() and property_yalign(), which are deprecated in GTK+.

GNOME/gtkmm,johne53/MB3Gtkmm,johne53/MB3Gtkmm,johne53/MB3Gtkmm,GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm