Rebuild structure so that priv is correctly linked

[nerandell]

The problem is referred here:

https://groups.google.com/forum/#!topic/elixir-lang-talk/9TmuUv3y9_g

Basically, when the binary application is used as a dependency, the priv directory is not linked. Mix links priv directories before actual compilation is done. On subsequent compilations, it works, because then the priv directory is generated already from the previous run.