Load tools.reader at run-time instead of compile-time [IMMUTANT-240]

We need to do this because codecs.clj gets loaded by the
ModuleClassLoader for the common module, which can't see the
deployment's CL that provides clojure. Clojure calls getClass() on the
current CL for every import, which won't work for clojure.lang.* from
the common module CL.