Circular and square maps should have the same area

[elexis]

The mapsize gamesetup setting (that only works with random maps) should yield the same map area independent from the map shape (square or circular).

A square map will have the size x² while a circular map will become pi * (x/2)².

Thus the area of a square map is4/pi times larger (+27%) than a circular map. (This may account for some "new a21 lag").

The change should likely be done in the rmlib, not every random map script.

While most square maps should become circular, we don't want to remove but improve the support of square maps.