Merge branch 'jk/clone-unborn-head-in-bare'

"git clone" from a repository whose HEAD is unborn into a bare
repository didn't follow the branch name the other side used, which
is corrected.

* jk/clone-unborn-head-in-bare:
  clone: handle unborn branch in bare repos

diff --cc builtin/clone.c
Simple merge

diff --cc t/t5702-protocol-v2.sh
Simple merge