REPL evaluation of conditional reader forms fails

When using reader conditionals, evaluating a reader conditional in a vanilla command-line REPL (not nRepl or anything like that) results in a "Conditional read not allowed" error message.

Loading the whole file with load-file works as expected.

This breaks the very normal workflow of eval-ing forms from a *.cljc file in a Clojure repl using (e.g.) inferior lisp.

Approach: clojure.main/repl (also used by swank I think) enables reader conditionals at the REPL.

Patch: clj-1700.patch