"git fetch --recurse-submodules" may not fetch the necessary commit
that is bound to the superproject, which is getting corrected.

* sb/submodule-recursive-fetch-gets-the-tip:
  fetch: ensure submodule objects fetched
  submodule.c: fetch in submodules git directory instead of in worktree
  submodule: migrate get_next_submodule to use repository structs
  repository: repo_submodule_init to take a submodule struct
  submodule: store OIDs in changed_submodule_names
  submodule.c: tighten scope of changed_submodule_names struct
  submodule.c: sort changed_submodule_names before searching it
  submodule.c: fix indentation
  sha1-array: provide oid_array_filter