add nip2 loadable-formats support, some fixes
add nip2 loadable-formats support, some fixes

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