* bzrlib/tests/test_selftest.py: (TestTestCaseWithMemoryTransport.test_make_branch_and_memory_tree, TestTestCaseWithMemoryTransport.test_make_branch_and_memory_tree_with_format): Inline previous calls to fail[Unless|If]ExistsOnDisk and clearly explain their aim.
* bzrlib/tests/__init__.py: (TestCaseWithMemoryTransport.failUnlessExistsOnDisk, TestCaseWithMemoryTransport.failIfExistsOnDisk): Deleted. They were more confusing than helpful.