power: Include sector maximum population in power factor

power: Include sector maximum population in power factor

Replace the term

    power value of materials and cost + 9

by

    power value of materials and cost + maximum population / 1000 * 8 + 1

The value of ordinary sectors (maximum population 1000) doesn't
change.  The stock game's mountains, plains and bridges are now worth
only 28% as much.

This concludes my tweaking of the power factor for now.  I tested it
with data from a real game (Hvy Metal II).  The effect is small: #5
overtakes #4, and the lead of #1 over #2 and #3 shrinks some.  Closer
analysis finds the following reasons.  The game had very expensive big
cities.  Valuing them correctly gives countries with many cities a
noticeable boost.  Planes are worth less than before, but the
difference is much larger for cheap planes.  Big piles of construction
materials are worth much less, and shells, guns and bars are worth
more.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>