Drive-by optimization of blur_surface()
Drive-by optimization of blur_surface()

tulcod/wayland,eyolfson/wayland,eyolfson/wayland,Tarnyko/weston-xdg_surface_present,mchalupa/wayland,mchalupa/wayland,bitfactor/wayland,kwm81/weston,udoprog/weston,Fantu/compositor-spice,sir-murray/wayland,abooij/wayland,jonnylamb/weston,abooij/wayland,mchalupa/weston,sir-murray/wayland,Fantu/compositor-spice,abooij/wayland,sir-murray/wayland,krezovic/weston,mchalupa/wayland,giucam/weston,Gnurou/weston,jonnylamb/weston,eyolfson/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,tulcod/wayland,bitfactor/wayland,kwm81/weston,eyolfson/weston,krezovic/weston,xorgy/weston,udoprog/weston,sir-murray/weston,giucam/weston,mchalupa/weston,xorgy/weston,eyolfson/wayland,sir-murray/weston,Gnurou/weston,bitfactor/wayland,tulcod/wayland