Merge branch 'mh/ref-api-3' into next

Merge branch 'mh/ref-api-3' into next

* mh/ref-api-3:
  is_refname_available(): reimplement using do_for_each_ref_in_array()
  names_conflict(): simplify implementation
  names_conflict(): new function, extracted from is_refname_available()
  repack_without_ref(): reimplement using do_for_each_ref_in_array()
  do_for_each_ref_in_array(): new function
  do_for_each_ref(): correctly terminate while processesing extra_refs
  add_ref(): take a (struct ref_entry *) parameter
  create_ref_entry(): extract function from add_ref()
  parse_ref_line(): add a check that the refname is properly formatted
  repack_without_ref(): remove temporary
  Rename another local variable name -> refname