The integration_test directory mocks a small hg repository. It
contains a list of subdirectories, each representing the state of the
repository at each commit.

The integration test script replays the "commit subdirectories" in
alphabetical order, and calls "pyre check; pyre incremental" until it
hits the tip. No specific naming scheme is required for the
subdirectories, but the format "commit_XXX" is strongly
encouraged. You can also append a suffix to the directory name if you
want to encode extra information in the directory name.

"commit_000" should always be the first directory, since that "empty
commit" is used to initialize the repository.

To add new commits, add a new directory with a name that follows the
current last. Add the python files you want to test, and make sure to
copy the control files (.pyre_configuration, .watchmanconfig) as well.
