all tested and working
all tested and working

revised formula for in/out/dest-in/dest-out, for vector and scalar paths

see https://github.com/libvips/libvips/issues/1301

jcupitt/libvips,lovell/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips,jcupitt/libvips,jcupitt/libvips,lovell/libvips