[freeciv-ai] RFC: another fstk cleanup

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

This cleanup does introduce some behaviour changes, and those haven't been
tested, so beware. This is mostly a request for some debate on this code.

It does:
 - fix some comments, add some comments
 - stop ships from whacking cities we can't occupy
 - don't assume enemy will build city walls
 - removed GB's /* FIXME: What if too far to walk? */ since this _is_
   checked later in the code (see if (move_time > THRESHOLD))
 - removed two duplicate ai_fuzzy()s
 - replaced GB's erronous comment /* This is strange. Why don't we kill a
   helpless enemy? -- GB */, as vuln==0 is used to denote that there is no
   defender and we can't occupy the city.
 - use two new macros: CAN_OCCUPY and IS_ATTACKER to make some hard to
   read code a little more obvious

  - Per

fstk1.diff
Description: Text document