Actual abilities of ships, planes and land units depend almost
completely on the individual unit's tech, not the nation's tech. The
power factor should reflect that.
The power value of a unit is of the form
base value * (20 + nation's tech level) / 500
Change it to
base value * (20 + unit's tech level) / 500
Note that a plane's base value still depends on the nation's tech
level. This commit merely makes the absurdity stand out a bit more.
To be fixed later.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>