Do not use a string literal when a format string is expected

Otherwise we'll get compiler errors.

Based on a patch by: Vincent Le Garrec <legarrec.vincent@gmail.com>

https://bugzilla.gnome.org/show_bug.cgi?id=696749

gio/gregistrysettingsbackend.c

@@ -228,7 +228,7 @@ g_message_win32_error (DWORD result_code,
   if (result_code == ERROR_KEY_DELETED)
     trace ("(%s)", win32_message);
   else
-    g_message (win32_message);
+    g_message ("%s", win32_message);
 };