[Freeciv] Not building certain city improvements by default

[Richard Stallman <rms@xxxxxxx>]

I never build marketplaces, since I am nearly always running the
largest science ratio possible, and as far as I can tell they do
little or no good in that situation.  It would be nice if I could
specify an option to tell the game never to choose marketplaces by
default.

I would like to suggest a feature where you can mark various city
options as disabled for default use, so that they won't get built
unless you select them explicitly.