Re: [PATCH 4/6] submodule--helper update-clone: allow multiple references

-               ${reference:+--reference "$reference"} \
+               ${reference:+"$reference"} \

Note how this changed the API of the submodule--helper.
Currently we pass in --reference $reference
and $reference consists of the string "--reference" and the actual
reference. So it looked like '--reference' '--reference=foo'

That is why we can pass the argument unseen to clone in the helper
via

    argv_array_push(&child->args, suc->reference);

This is fixed now.