-> No longer install graphical packages if the xserver is disabled.
-> avoid duplication of "mkIf config.services.xserver.enable".
svn path=/nixos/branches/modular-nixos/; revision=16044
disabled. Other desktop/display/window manager modules should be
conditional on config.services.xserver.enable as well, but at least
they're disabled by default due to other options.
svn path=/nixos/branches/modular-nixos/; revision=16031