Merge branch 'jt/clone-unborn-head'

"git clone" tries to locally check out the branch pointed at by HEAD of the remote repository after it is done, but the protocol did not convey the information necessary to do so when copying an empty repository. The protocol v2 learned how to do so. * jt/clone-unborn-head: clone: respect remote unborn HEAD connect, transport: encapsulate arg in struct ls-refs: report unborn targets of symrefs