Wait for a reply in thunar-settings.

If we don't do this the call fails when the thunar service is not
running yet... Lame...

thunar/thunar-settings

@@ -2,5 +2,5 @@
 
 test "x$DISPLAY" != "x" || DISPLAY=:0
 
-dbus-send --session --dest=org.xfce.FileManager /org/xfce/FileManager \
-    org.xfce.FileManager.DisplayPreferencesDialog "string:$DISPLAY"
+dbus-send --session --print-reply --dest=org.xfce.FileManager /org/xfce/FileManager \
+    org.xfce.FileManager.DisplayPreferencesDialog "string:$DISPLAY" 1> /dev/null