power plant economics

```
I see in the log you seem to be changing things about power plant types the ai
builds.
For what it's worth, I always avoid the nuclear plant if I have a chance to do
so. The fusion plant has the best ratios of energy per worker and energy per
space, the solar plant is somewhat inferior, and the nuclear plant is much
worse. Energy per worker tends to be the most important factor. The nuclear
plant seems to have few hitpoints due to its low cost. Their large number will
also cover a large area. Both matters a lot in ground battles. The nuclear
plant has only (not much) better ratio of money per energy. So the ai logic
should be simple - if available, always build fusion plant, if not, always
build solar plant, only if also not, nuclear plant.
```

Original issue reported on code.google.com by `anonymis...@arcor.de` on 21 Nov 2014 at 5:59