[MERGE] Convert tests.blackbox.test_d* to use internals where appropriate

[John Arbash Meinel]

John Arbash Meinel has voted resubmit.
Status is now: Resubmit
Comment:
 From what I can tell, the tests are actually designed to run a similar 
"diff" test, but using different example branches (by overriding 
make_example_branch()).

Which means that this change will breaks the point of the tests. 
(Instead of running the tests 2 times with slightly different data, you 
will run it 2 times with identical data).

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C46B85595.7090800%40warwick.ac.uk%3E