matcher: make e.g. 'relpath:.' lead to fast paths Several commands take the fast path when match.always() is true. However, when the user passes "." on the command line, that results in a matcher for which match.always() == False. Let's make it so such matchers return True, and have an empty list of .files(). This makes e.g. "hg log ." as fast as "hg log" and "hg revert ." as fast as "hg revert --all" (when run from repo root).