Merge branch 'vs/submodule-clone-nested-submodules-alternates'

Merge branch 'vs/submodule-clone-nested-submodules-alternates'

"git clone --reference $there --recurse-submodules $super" has been
taught to guess repositories usable as references for submodules of
$super that are embedded in $there while making a clone of the
superproject borrow objects from $there; extend the mechanism to
also allow submodules of these submodules to borrow repositories
embedded in these clones of the submodules embedded in the clone of
the superproject.

* vs/submodule-clone-nested-submodules-alternates:
  submodule--helper: set alternateLocation for cloned submodules