cleanup after test runs
add nock as devDependency
Fully tested and coveraged util.js

![coverage
report](http://f.cl.ly/items/423h0v0u3P3K0u2F2e05/Screen%20Shot%202013-1
1-18%20at%206.17.39%20PM.png)
fix async test
test caching of downloadable files as well