* gofmt ui.go
* Refactor Nav API around symlinks handling (mostly)
1. Get both `Lstat` and `Stat` while reading the files. Stat info is
used by default, but we still can tell it's a link if needed.
2. Remove all other `Stat` calls from different places.
3. Handle hidden files while reading.
4. `currFile` now returns error if there are no files.
5. `currEmpty` and `currPath` not longer necessary, removed.
6. `open` now returns a named error ErrNotDir, where expected.
7. Side effect: Links that point at directories are now sorted among
"actual" directories.
