Exclude clojure in all default dependencies

[lsnape]

The clojure version included by one of my default dependencies was loaded before the clojure version defined in the project by BOOT_CLOJURE_VERSION, without any warning or trace.

The workaround is to exclude clojure from all the default dependencies, but ideally clojure should be excluded by boot automatically.

[micha]

See #230, it's related.

[micha]

I think the correct solution is to add an explicit org.clojure/clojure dependency to your :dependencies in the build.boot file. I think there should be a warning, though. What do you think?