A new submodule helper "git submodule embedgitdirs" to make it
easier to move embedded .git/ directory for submodules in a
superproject to .git/modules/ (and point the latter with the former
that is turned into a "gitdir:" file) has been added.
* sb/submodule-embed-gitdir:
worktree: initialize return value for submodule_uses_worktrees
submodule: add absorb-git-dir function
move connect_work_tree_and_git_dir to dir.h
worktree: check if a submodule uses worktrees
test-lib-functions.sh: teach test_commit -C <dir>
submodule helper: support super prefix
submodule: use absolute path for computing relative path connecting