Merge branch 'gg/worktree-from-the-above'

In a non-bare repository, the behavior of Git when the
core.worktree configuration variable points at a directory that has
a repository as its subdirectory, regressed in Git 2.27 days.

* gg/worktree-from-the-above:
  dir: minor refactoring / clean-up
  dir: traverse into repository

diff --cc dir.c
Simple merge