Removed -Wunderspec from the Makefile

Although it sounded -Wunderful, it was in fact giving us a dialyzer
error that really didn't help anyone.
updated chef_user:new_record/3 spec

The final clause actually sends a {null, null, null} tuple as the third
argument, but the spec only expected {binary(), binary(), binary()}.
Merge pull request #68 from opscode/jd/dialyzer-fix

Dialyzer Fix