Merge branch 'nd/worktree-cleanup-post-head-protection'

Merge branch 'nd/worktree-cleanup-post-head-protection'

Further preparatory clean-up for "worktree" feature continues.

* nd/worktree-cleanup-post-head-protection:
  worktree: simplify prefixing paths
  worktree: avoid 0{40}, too many zeroes, hard to read
  worktree.c: use is_dot_or_dotdot()
  git-worktree.txt: keep subcommand listing in alphabetical order
  worktree.c: rewrite mark_current_worktree() to avoid strbuf
  completion: support git-worktree