power: Saner power value for tech, particularly at low tech

power: Saner power value for tech, particularly at low tech

In the old times, power didn't consider tech at all.  Chainsaw's
option NEWPOWER (mandatory since v4.2.14, on by default before)
changed this dramatically: the power factor gets multiplied by
max(1, tech) / 500.

In the early game, small absolute tech differences yield large power
factor differences.  For instance, if country A has tech level 10, and
B has 5, then A gets a factor two boost.

As the game progresses, tech differences between viable countries tend
to grow, but only slowly.  The influence on power diminishes.  For
instance, if C has tech level 270 and D has 240 (quite a respectable
tech lead), then C gets a modest 1.125x boost over D.

Change the factor to (20 + tech) / 500.  Now A's advantage is only
1.2, and C's is 1.115.

You might think that's rather low.  However, tech is not power unless
you project it, and then it manifests itself as sectors, population
and other stuff power counts.

The same tech term occurs in plane power, except with just tech
instead of max(1, tech) .  Change it there as well, for consistency.

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