TODO list for AI v3.0

This is mostly a repost of an earlier post, updated to the most recent
code. A good way to learn how it works is to make small changes to it.
Here is a list of the smaller changes the AI needs desperately:
 - AI builds cities without regard to danger at that location. Make that
stop. Use movemap code to find dangers.
 - AI doesn't know how to make trade routes or when.  It should try to
build trade routes for its best cities (most building bonuses and
least corruption) by moving caravans there and changing homecity.
 - Convert more AI code to pf (common/aicore/path_finding.c), in
particular the bodyguard code.
 - The AI should clean up more pollution. See
http://rt.freeciv.org/Ticket/Display.html?id=82
 - workers starve their cities, and rarely build irrigation
 - (PR#814) engineers (settlers?) do not irrigate/upgrade cities' terrain
(their city center) when in mode auto-settler
 - (PR#1490) Wonder obsolescence / AI tech goals. The AI should not be so
eager to research techs that would obsolete existing wonders that it has.
(And maybe be more eager to research techs that obsolete enemy wonders?)
This is particularily important concerning Great Library.
  - Make the AI increase lux rates to handle city disorder on a grand
scale better. See FIXME in tax code.
  - Make AI build explorers. Just add a function that evaluates the best
unit to build as explorer, then add some wild ass guess (WAG) as to how
much we want it, perhaps based on amount of unexplored terrain. First
check if the continent is fully explored, though.  That is already done in
aidata.c.

  - Per