Added a couple of tests

[akaranta]

Added tests for compare-and-set! and (by-ref)

[dmiller]

Unfortunately, cannot accept patches / pull requests unless you have contributor's agreement on file with Clojure central.

Also, I prefer to follow the outlines for creating issues and attaching patches set forth on dev.clojure.org.

[akaranta]

     Hi,

I made these patches a while ago and back then being quite new to clojure
clr am not sure if they are any good. Anyhow, for future needs I signed the
Clojure contributor agreement and will use dev.clojure.org for further
issues+patches.

          ::Antti::