[freeciv-data] Precolumbian, Classical, Asiatic, European

Why not add more kind of civ (like Precolumbian, Classical, Asiatic, European 
) or more over, the problem is in the nation/*.ruleset -> city_style, if add 
more possiblity, all old tiles run with make more error ??
But in other hand, the graphics are ok in some tiles.

Thank Fred.