Mention that there's no way to undo it.
https://bugzilla.gnome.org/show_bug.cgi?id=654239
* (such as the various fundamental type implementations or the signal
* system).
*
- * This function is idempotent.
+ * This function is idempotent: If you call it multiple times, all but
+ * the first calls will be silently ignored.
+ *
+ * There is no way to undo the effect of g_type_init().
*
* Since version 2.24 this also initializes the thread system
*/