test-status-rev: document one more broken test
The status for missing_content2_content2-untracked doesn't get
reported at all. Since the file does exist in the working copy, it
should reported as unknown. Document that in the test.
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.