Changes contributed by Durk Talsma:

Changes contributed by Durk Talsma:

Here's a few changes I made to fg-0.58 this weekend. Included are the
following features:
- Sun and moon have a halo
- The moon has a light vector, moon_angle, etc. etc. so that we can have
  some moonlight during the night.
- Lot's of small changes tweakes, including some stuff Norman Vine sent
  me earlier.