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