Merge branch 'nd/worktree-name-sanitization'

In recent versions of Git, per-worktree refs are exposed in refs/worktrees/<wtname>/ hierarchy, which means that worktree names must be a valid refname component. The code now sanitizes the names given to worktrees, to make sure these refs are well-formed. * nd/worktree-name-sanitization: worktree add: sanitize worktree names