Make recursive build-deps programmatic and independent from the shell

[jaccarmac]

I found out the hard way that build-deps can be tricky to use on a tiny embedded system. In my case, I was trying to build a project which uses voom dependencies on a Raspberry Pi. I simply dumped the lein script in my home directory and tried to build using ~/lein voom build-deps. This failed during the recursive build-deps step because, apparently, it calls lein voom build-deps instead of using an API.

The solution is trivial on something like a Pi: dump the script into a place where your shell can find it, and you're golden. However, on systems where this is harder to do (Docker containers, which don't have "real" shells, come to mind) it could be a problem. Arguably, we shouldn't be using something like the JVM in something so small, but it would be nice for the plugin not to depend on its environment (that is, once lein launches, it becomes its own environment).

[jaccarmac]

One more thing I forgot to point out. On a Pi, the main barrier to Clojure performance is the start-up time of the JVM. Once lein starts running, it's actually relatively fast, but making it call itself multiplies the time spent waiting for Java to spin up by the number of things you have to build.