fixed missing textdomain declaration for preferences_display

po/wesnoth-lib/POTFILES.in

@@ -6,6 +6,7 @@ src/mapgen_dialog.cpp
 src/marked-up_text.cpp 
 src/minimap.cpp
 src/preferences.cpp
+src/preferences_display.cpp
 src/show_dialog.cpp
 src/widgets/file_chooser.cpp
 src/editor/editor_dialogs.cpp

src/preferences_display.cpp

@@ -12,6 +12,8 @@
 */
 #include "global.hpp"
 
+#define GETTEXT_DOMAIN "wesnoth-lib"
+
 #include "display.hpp"
 #include "gettext.hpp"
 #include "hotkeys.hpp"