[Freeciv-Dev] (PR#13029) wanted: unavailable nations shouldn't be shown

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=13029 >

There are two flags for nations that can't be picked: is_unavailable and
is_used.

is_used means, naturally, that another player is using the nation and it
cannot be chosen.

is_unavailable means this scenario doesn't allow this nation at all.

The latter choice shouldn't be shown at all in the nation selection
dialog.  Right now unavailable nations are shown just like used nations,
with a line through them.  This is clearly bad (in most scenarios almost
all of the nations will be unavailable; it may be hard just to find an
available one).

-jason