Fixed a nasty bug where some terrain values were getting nan (in fact
because the terrain equations weren't differentialbe at some points!).
Wind is now pretty much working (tuning can wait).

-Peter Mawhorter
Lots of progress on weather: got a basic form of cloud potential
simulation working, and with a few tweaks it could be acceptible.
Encountered more bugs with the dicontinuity of smooth() at 0, so I
changed smooth to use exp() as its basis instead of pow(). Accordingly I
re-did all of the smooth() parameters, although I haven't done the ones
in geology.[ch] yet.

There's also a new bug that shows up as faint lines on the world map.
Have to look into that, but it appears to be part of the base trig
components used in continents and the like.

-Peter Mawhorter