[Freeciv] info on rules change: city names

["Per I. Mathisen" <per@xxxxxxxxxxx>]

A new default rule has been added to the cvs version of freeciv (1.13.1).

A player can no longer have two cities with the same name.

This feature can be deactivated or altered through the "set citynames X"
server option. If set to 0, there are no restrictions (like before). If
set to 1 (new default), city names have to be unique to a player. If set
to 2 or 3, city names have to be globally unique. If set to 3, a player
also isn't allowed to use a default city name of another nation.

Yours
Per