(PR#11777) Cleanup of AI tech code

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=11777 >


From cvs log:
Backport: Divide tech want used in AI diplomacy exchange calculations by
game turn, as tech want is a value that is continually accumulated, and
in late games you might see the AI exchanging nearly all its cities for
a few techs. Fix is part of PR#11777.

What happens after saving & loading?
--
mateusz