gegl: Update code to work with gegl-0.3 (GEGL master)
gegl: Update code to work with gegl-0.3 (GEGL master)

achadwick/libmypaint,achadwick/libmypaint,achadwick/libmypaint,b3sigma/libmypaint,achadwick/libmypaint,b3sigma/libmypaint,b3sigma/libmypaint