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