[freeciv-ai] active ai diplomats

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

This is hopefully the last version. Lots of bugs fixed. Lots of small
improvements. Uses bodyguards when available (rare). Tried allowing use of
slower bodyguards, hacked up gode to rendezvous, but that worked poorly.
Properly increases taxes if necessary right before we try to incite a
city. Sets the unit role properly to distinguish between defense and
offensive actions.

Some notable collateral changes
 - I've introduced the use of (-1, -1) as invalid goto coordinates, and
the AI macro HAS_GOTO(punit) to check for this, which has been littered
around the AI code to stop coredumps
 - New convenience function ai_unit_ready(punit) which clears all
previously assignments and sets the unit to (in)sane defaults
 - A few changes to logging for even more detailed info (yay!)
 - Small cleanup of bodyguarding code
 - We no longer set punit->ai.ai_role to AINUNIT_NONE each turn (which is
so broken)

Please test and review.

Yours
Per

"I don't see why people are so upset about cloning sheep. American
television networks have been doing that to their audiences for years."
-- Jello Biafra

activediplong2.diff
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