revert: don't assume ignored files will be returned in the unknown list
That's just an artifact of the current implementation, and I'll change
that soon.
Bonus points:
- we don't care about the unknown list at all
- we don't print an extra message if we try to revert a removed file
that is not present in the target revision
% should fail
abort: path contains illegal component: .hg/00changelog.i
adding a/a
% should fail
abort: path 'b/b' traverses symbolic link 'b'
% should succeed
% should still fail - maybe
abort: path 'b/b' traverses symbolic link 'b'