add DX dir to project settings (only for dx builds of course) for the situation that the DirectX installer did not put them into the global VS settings (which it never does on my system)
add DX dir to project settings (only for dx builds of course) for the situation that the DirectX installer did not put them into the global VS settings (which it never does on my system)

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@1898 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok