match: handle everything-matching using new alwaysmatcher
Having a special matcher that always matches seems to make more sense
than making one of the other matchers handle the case. For now, we
just use this new matcher when no patterns were provided.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.