Add a couple of more variable bindings, make all the set visual gear values optional, to allow skipping trailing params or specifying ones in the middle as nil to not set. Should make using it more convenient in simple cases.

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})