[CR] Map-extra global reduction

If I read that code right, this PR reduces the map-special rate on roads and fields to that in buildings and underground: somewhat rarer.  Hopefully this'll quell the complaints about excessive amounts of corpses.  Granted, it'll reduce the amount of other Neat Stuff too.

If you like, I can see about reducing the National Guard's gear-issue while I'm at it.  I'm not thrilled at the idea, personally.