GTK+ 3.15.10 Brings Better Wayland Support

GTK+ 3.15.10 brings updates to the GtkFileChooser, GtkWindow, Printing, Wayland, and GL components. As such, the GdkGears example has been ported to the modern OpenGL library, Avahi-browsed printers are correctly handled, printer state is now correctly set, and window dragging on header bars has been improved.