match: optimize visitdir() for when no explicit files are listed In patternmatcher, we used to say that all directories should be visited if no explicit files were listed, because the case of empty _files usually implied that no patterns were given (which in turns meant that everything should match). However, this made e.g. "hg files -r . rootfilesin:." slower than necessary, because that also ended up with an empty list in _files. Now that patternmatcher does not handle includes, the only remaining case where its _files/_fileset fields will be empty is when it's matching everything. We can therefore treat the always-case specially and stop treating the empty _files case specially. This makes the case mentioned above faster on treemanifest repos.