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.
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown