Handle Clojure dependency in better way

[Deraen]

<michaniskin> i think boot should handle the case of mismatched clojure versions better
<michaniskin> like maybe warn if BOOT_CLOJURE_VERSION is different than a clojure version set in :dependencies
<michaniskin> or something
<michaniskin> i wonder if maybe we add BOOT_CLOJURE_VERSION to :dependencies automatically?

[micha]

See #232, it's related.

[martinklepsch]

i wonder if maybe we add BOOT_CLOJURE_VERSION to :dependencies automatically?

Maybe we do that, but also add a warning that it's "good practice" to pin it on your own?