protocol: Make it clear that returned "one-shot" objects are destroyed
protocol: Make it clear that returned "one-shot" objects are destroyed

The objects returned by the frame and sync request are destroyed by the
compositor after the "done" event on the wl_callback interface is fired.

tulcod/wayland,mchalupa/wayland,mchalupa/wayland,abooij/wayland,sir-murray/wayland,sir-murray/wayland,bitfactor/wayland,abooij/wayland,eyolfson/wayland,sir-murray/wayland,eyolfson/wayland,tulcod/wayland,tulcod/wayland,mchalupa/wayland,bitfactor/wayland,eyolfson/wayland,abooij/wayland,bitfactor/wayland