Adding an option to disallow committers from approving their own code.

Our company needs to implement the policy that a developer cannot merge their own code.  Adding this option allows us to create a build that would only work when triggered and the commentor is listed as Admin and isn't in the commit list.  

I am not sure how to develop the test to mock commits in the pull request, and if someone can point me in the right direction I would be happy to add some tests surrounding it.