Add protocol references in the loader.

These are currently ignored, because they are only important when the
runtime has upgraded the protocol.  The runtime will upgrade legacy
protocols, but they are not referenced by this indirection layer.

loader.c

@@ -105,6 +105,8 @@ struct objc_init
 	struct objc_category *cat_end;
 	struct objc_protocol2 *proto_begin;
 	struct objc_protocol2 *proto_end;
+	struct objc_protocol2 **proto_ref_begin;
+	struct objc_protocol2 **proto_ref_end;
 };
 // end: objc_init
 #include <dlfcn.h>