Use in-ns when creating the repl

This avoids blowing away any :exclude lists in :refer-clojure or :use
statements resulting in clojure.lang.Namespace.warnOrFailOnReplace
errors.

e.g.

        ;; foo.clj
        (ns foo
          (:refer-clojure :exclude [defn]))

        (defmacro defn [& args] nil)

        ;; bar.clj
        (ns bar
          (:require [foo :refer [defn]])
          (:refer-clojure :exclude [defn]))

        (defn example [])

Running :Repl from bar.clj results in:

IllegalStateException defn already refers to: #'foo/defn in namespace: bar
clojure.lang.Namespace.warnOrFailOnReplace (Namespace.java:88)
Merge pull request #21 from guns/in-ns

Use in-ns when creating the repl