Possibly detect wrong versions of tools.namespace

[martinklepsch]

I by accident had a wrong version of tools.namespace on my classpath (0.2.7) which cause .cljc files to be ignored when running with :language :clojure. It continued to work with :language :clojurescript.

Not sure how easy it would be to detect this but it could improve the experience of using Codox to check that the right version of tools.namespace is used.