Major update to vips and nip2 to 8.0.2, changes:

- Much better conversion to greyscale
- More efficient use of file descriptors
- Rewritten TIFF pyramid creator
- Removed old stuff

See http://libvips.blogspot.co.uk/2015/05/whats-new-in-80.html
and https://github.com/jcupitt/libvips/blob/master/ChangeLog