Move away from g_type_class_add_private()
g_type_class_add_private() will be deprecated in GLib 2.58. Replace:
- g_type_class_add_private() with G_DEFINE_TYPE_WITH_PRIVATE()
- G_TYPE_INSTANCE_GET_PRIVATE() with *_get_instance_private()
No IPv6 SupportCurrently Leak Resolver Objects Due To Messy Allocation Path