2nd try... just shortcircuit most of onGameTick20 when we are between turns.
foreach(dir
Fonts
Forts
Graphics
Locale
Maps
Missions
Music
Names
Scripts
Sounds
Themes
misc
)
add_subdirectory(${dir})
endforeach(dir)
if(${GL2})
add_subdirectory(Shaders)
endif(${GL2})