[PATCH/POC 0/7] Support multiple worktrees

This is what I imagine multi worktree support (aka git-new-workdir)
looks like. Basically two variables will control access to the repo:
$GIT_SUPER_DIR for worktree specific stuff and $GIT_DIR for the rest.

I like the idea of using git_path() to hide path relocation caused by
GIT_SUPER_DIR, but I may have made some design mistakes here..
setup_git_directory() changes are hairy. It's not surprise if I broke
something in there. Not important for a PoC though.

Final series may be a few patches longer as I only lay the foundation
in this series.

Nguyễn Thái Ngọc Duy (7):
  Make git_path() beware of file relocation in $GIT_DIR
  Add new environment variable $GIT_SUPER_DIR
  setup.c: add split-repo support to .git files
  setup.c: add split-repo support to is_git_directory()
  setup.c: reduce cleanup sites in setup_explicit_git_dir()
  setup.c: add split-repo support to setup_git_directory*
  init: add --split-repo with the same functionality as git-new-workdir

 builtin/init-db.c     |  42 +++++++++++++++
 cache.h               |   5 ++
 environment.c         |  37 ++++++++++++--
 path.c                |  45 ++++++++++++++--
 setup.c               | 139 ++++++++++++++++++++++++++++++++++----------------
 t/t0060-path-utils.sh | 115 +++++++++++++++++++++++++++++++++++++++++
 test-path-utils.c     |   7 +++
 trace.c               |   1 +
 8 files changed, 339 insertions(+), 52 deletions(-)

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1.8.5.1.77.g42c48fa