Fix refer-clojure at the top level

[arrdem]

Since refer is now deprecated, and refer* is private, refer-clojure cannot (correctly) macroexpand to a refer* invocation outside of the ns form where it is sanboxed within a fn compiled in clojure.core. Rather than implement refer-clojure as a macro and conditionally employ the same (with-ns clj (eval)) tactic used by ns, this patch simply makes refer-clojure a fn which invokes refer*.

Fixes #132