Currently it is possible to override clojure.core/in-ns and clojure.core/ns, but it is not possible to refer to the namespace-specific vars without fully qualifying them:
`
user=> (ns foo (:refer-clojure :exclude [in-ns]))
nil
foo=> (def in-ns 1)
'foo/in-ns
foo=> in-ns
<clojure.lang.RT$1@76b5e4c5>
`
After this patch, overriding in-ns and ns works like for every other clojure.core var:
`
user=> (ns foo (:refer-clojure :exclude [in-ns]))
nil
foo=> (def in-ns 1)
'foo/in-ns
foo=> in-ns
1
`
