Merge branch 'ab/ref-filter-leakfix'

"git for-each-ref" family of commands were leaking the ref_sorting
instances that hold sorting keys specified by the user; this has
been corrected.

* ab/ref-filter-leakfix:
  branch: use ref_sorting_release()
  ref-filter API user: add and use a ref_sorting_release()
  tag: use a "goto cleanup" pattern, leak less memory