display circle for custom build dist values, display nothing if no limit. map borders are not taken into account at this point
foreach(dir "Fonts" "Forts" "Graphics" "Locale" "Maps" "Music" "Sounds" "Themes" "Missions" "Names" "misc" "Scripts")
add_subdirectory(${dir})
endforeach(dir)
if(${GL2})
add_subdirectory(Shaders)
endif(${GL2})