Merge branch 'es/worktree-repair'

Merge branch 'es/worktree-repair'

"git worktree" gained a "repair" subcommand to help users recover
after moving the worktrees or repository manually without telling
Git.  Also, "git init --separate-git-dir" no longer corrupts
administrative data related to linked worktrees.

* es/worktree-repair:
  init: make --separate-git-dir work from within linked worktree
  init: teach --separate-git-dir to repair linked worktrees
  worktree: teach "repair" to fix outgoing links to worktrees
  worktree: teach "repair" to fix worktree back-links to main worktree
  worktree: add skeleton "repair" command