improve im_compass() back compat
improve im_compass() back compat

jcupitt/libvips,lovell/libvips,mcanthony/libvips,jcupitt/libvips,leiyangyou/libvips,leiyangyou/libvips,wishabi/libvips,mcanthony/libvips,jcupitt/libvips,lovell/libvips,wishabi/libvips,leiyangyou/libvips,leiyangyou/libvips,wishabi/libvips,mcanthony/libvips,lovell/libvips,jcupitt/libvips,lovell/libvips,mcanthony/libvips,wishabi/libvips