Fred: adjust enemy_worth

Decrease it a little bit for factions other than Northerners.  For
Northerners, it won’t make much of a difference because the units are
cheap.
Fred: change how full offensive mode works

Don’t have the RCA AI take over any more.  Instead, we don’t rush down
the right any more in this case, which means that enemy_leader now
becomes the most important “collect it all” zone, resulting in the AI
units going for the enemy leader.