Merge branch 'ka/want-ref-in-namespace' into maint

"git upload-pack" which runs on the other side of "git fetch"
forgot to take the ref namespaces into account when handling
want-ref requests.

* ka/want-ref-in-namespace:
  docs: clarify the interaction of transfer.hideRefs and namespaces
  upload-pack.c: treat want-ref relative to namespace
  t5730: introduce fetch command helper