Either g_type_register_static_simple (used by G_DEFINE_TYPE_EXTENDED)
and G_IMPLEMENT_INTERFACE use automatic variables for GTypeInfo and
GInterfaceInfo structs, while tutorials and source code often use
static variables. This commit consistently adopts the former method.
https://bugzilla.gnome.org/show_bug.cgi?id=600158
Change default values returned by gtk_print_settings_get_printer_lpi()
and gtk_print_settings_get_resolution{_x, _y}(). New values are 150 for
lpi and 300 for resolution (instead of 0) (#590861).
