add missing func back

src/cljs/emptyhead/util/magic.cljs

@@ -9,5 +9,10 @@
 (defn thought-impl-prop [operator]
   (conj thought-impl-ns operator))
 
+(def extension-ns (conj thought-ns :extends))
+
+(defn extension-prop [stage]
+  (conj extension-ns stage))
+
 (defn symbolize-ns [ns]
   (str/join "." (map name ns)))