Revert "GObject: prevent installing properties after init"

This reverts commit ddb0ce1421.

Conflicts:
	gobject/gobject.c

https://bugzilla.gnome.org/show_bug.cgi?id=698614

gobject/gtype-private.h

@@ -70,7 +70,6 @@ void        _g_closure_invoke_va (GClosure       *closure,
 				  int             n_params,
 				  GType          *param_types);
 
-gboolean    g_type_is_in_init    (GType type);
 
 G_END_DECLS