Light changes learned while starting to understand multiple conflicts on
the same path.
* bzrlib/tests/test_conflicts.py:
(TestResolveUnversionedParent): These tests creates multiple
conflicts...
* bzrlib/help_topics/en/conflicts.txt:
Let's call a dir a dir not a file in 'Missing parent' doc.
* bzrlib/conflicts.py:
(_resolve_interactive): Clearer error message.