This tweak improves the uniformity of the generated patches of hat
tiling, by selecting from (the closest 32-bit approximation I can get
to) the limiting probability distribution of finite patches in the
whole plane.
This shouldn't invalidate any grid description that contains enough
coordinates to uniquely specify a piece of tiling - in particular, any
generated by the game itself. But if anyone's been brave enough to
hand-type a grid description in the last two days and left off some of
the coordinates, then those might be invalidated.
I renamed it in a hurry this morning after the first report of a git
error message on Windows. Now I realise that several source files
referred to the old name, and also need fixing.
