Merge branch 'jt/submodule-repo-is-with-worktree'

Merge branch 'jt/submodule-repo-is-with-worktree'

The logic to tell if a Git repository has a working tree protects
"git branch -D" from removing the branch that is currently checked
out by mistake.  The implementation of this logic was broken for
repositories with unusual name, which unfortunately is the norm for
submodules these days.  This has been fixed.

* jt/submodule-repo-is-with-worktree:
  worktree: update is_bare heuristics