Merge branch 'cw/worktree-relative'

An extra worktree attached to a repository points at each other to allow finding the repository from the worktree and vice versa possible. Turn this linkage to relative paths. * cw/worktree-relative: worktree: add test for path handling in linked worktrees worktree: link worktrees with relative paths worktree: refactor infer_backlink() to use *strbuf worktree: repair copied repository and linked worktrees