Fred: remove injured units case from village grabbing zone action

The retreat zone action takes care of that (and has been doing so for
quite some time).
Fred stop_unit CA: add moving injured units to villages

These are units which have nothing else to do, so we might as well move
them to villages for healing.  In most practical cases, this will
likely only affect the leader.
Fred: rename stop_unit CA to finish_turn

Since it does more than taking away moves and attacks now.
Fred: change rating for center zone when pulling in units from the left

So that they don’t get stuck behind the mountains.
Fred: reinstate previous unit filters for left, center, right

They control a lot more than just which units to consider when pulling
units into the zone.
Fred: select units with and without MP differently for a zone

Units with MP are taken from the entire map (except if
cfg.only_zone_units is set).  Units without MP need to be taken from
cfg.unit_filter only.
Fred: increase aggressiveness in leader_threat zone
Fred zone holding: remove calculation of dx and dy

They aren’t used any more.
Fred: remove an explicit side=1 definition

Needs to be current side, if this is ever to work more generally.
Fred zone holding: minor tweak to position rating
Fred: minor changes to debug messages
Fred: add village information to stats output
Fred village grabbing: only consider villages inside the zone

Previously it was set to all villages on the map, which screwed up
moves in other zones now that units are taken from everywhere.
Fred attacks: don't hardcode limits for acceptable attack outcomes
Fred attacks: tweaks to enemy_worth rating