Summary: Also change the internal API so it no longer accepts the "heads" argument.
Reviewed By: ryanmce
Differential Revision: D6745865
fbshipit-source-id: 368742be49b192f7630421003552d0a10eb0b76d
Many tests didn't change back from subdirectories at the end of the tests ...
and they don't have to. The missing 'cd ..' could always be added when another
test case is added to the test file.
This change do that tests (99.5%) consistently end up in $TESTDIR where they
started, thus making it simpler to extend them or move them around.
