[freeciv-ai] logging and ai explorer improvement patch

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

This patch primarily improves logging by providing and using some logging
macros (defined in aitools.h). These are rather inflexible in that they
don't take varargs (ie no "%s %d" messages), but they do output quite a
lot of useful info in a standardized way.

I intend to add a FERRY_LOG macro and a few new LOGLEVEL_* defines later,
unless someone beat me to it.

Also, while doing this, I fixed some calls to do_unit_goto() that didn't
check if we died, and made an AI's explorers get a homecity and return
home instead of standing idle out in the bush (that just looks so silly
and also explorers in a city can be important to defend it from attackers
early game).

Please read and criticize.

Yours
Per

logandexplore.diff
Description: Text document