Add tests for Shepherd conditionals

Hello @nicks, 

I don't really expect you to merge this now since there's nothing ot make the
tests pass, but I wanted to make it so that you can pick up after me with
conditionals, and to better define their expected behavior.

Please review the following commits I made in branch 'kyle-test-conditionals'.

1b5442260fccc721b12573a6a9d11b2138e3e6df (2013-08-13 20:40:10 -0700)
Add tests for Shepherd conditionals


R=@nicks