Attempt to fix objcAllocateClassPair() for root classes.

@David: Could you check whether I got this right?

runtime.c

@@ -684,11 +684,23 @@ Class objc_allocateClassPair(Class superclass, const char *name, size_t extraByt
 	// Create the metaclass
 	Class metaClass = gc->malloc(sizeof(struct objc_class));
 
+	if (Nil == superclass)
+	{
+		/*
+		 * Metaclasses of root classes are precious little flowers and work a
+		 * little differently:
+		 */
+		metaClass->isa = metaClass;
+		metaClass->super_class = newClass;
+	}
+	else
+	{
 		// Initialize the metaclass
 		// Set the meta-metaclass pointer to the name.  The runtime will fix this
 		// in objc_resolve_class().
 		metaClass->isa = (Class)superclass->isa->isa->name;
 		metaClass->super_class = superclass->isa;
+	}
 	metaClass->name = strdup(name);
 	metaClass->info = objc_class_flag_meta | objc_class_flag_user_created |
 		objc_class_flag_new_abi;
@@ -699,12 +711,21 @@ Class objc_allocateClassPair(Class superclass, const char *name, size_t extraByt
 	newClass->isa = metaClass;
 	// Set the superclass pointer to the name.  The runtime will fix this when
 	// the class links are resolved.
-	newClass->super_class = (Class)(superclass->name);
+	newClass->super_class = (Nil == superclass) ? Nil : (Class)(superclass->name);
+
 	newClass->name = strdup(name);
 	newClass->info = objc_class_flag_class | objc_class_flag_user_created |
 		objc_class_flag_new_abi;
 	newClass->dtable = uninstalled_dtable;
+
+	if (Nil == superclass)
+	{
+		newClass->instance_size = sizeof(struct objc_class);
+	}
+	else
+	{
 		newClass->instance_size = superclass->instance_size;
+	}
 
 	return newClass;
 }