Fred: putting units back out is now done by the counter attack eval function

Not needed here any more.  In fact, the removed code block didn’t do
anything.
Fred attacks: use forward attack outcome as starting point for counter attack eval

Use the average hitpoints of the forward attack on all units before
calculating the counter attack.  This is approximate, but the exact
method is too expensive and this is better than doing nothing.
Fred attacks: it's ok for regenerating leaders to get poisoned

Don’t blacklist an attack if the AI leader might get poisoned, but
regenerates and all other stats are acceptable.