Merge pull request #2650 from metabase/massive-performance-improvement

Don't fetch *current-user* just to check superuser status 

src/metabase/api/common.clj

@@ -65,7 +65,7 @@
 (defn check-superuser
   "Check that `*current-user*` is a superuser or throw a 403."
   []
-  (check-403 (:is_superuser @*current-user*)))
+  (check-403 (db/exists? 'User, :id *current-user-id*, :is_superuser true)))
 
 
 ;;; #### checkp- functions: as in "check param". These functions expect that you pass a symbol so they can throw exceptions w/ relevant error messages.