Fix build by making the registry guarded by an ArcMutex.

src/intermediate/regular_link.rs

@@ -13,7 +13,7 @@ intermediate!(IRegularLink, RegularLink, original, registry, {
     let children = {
         let mut ret = Vec::new();
         for obj in original.children.iter() {
-            ret.push(IObject::new(registry, obj).await?);
+            ret.push(IObject::new(registry.clone(), obj).await?);
         }
         ret
     };