Merge branch 'ps/refs-for-each'

Merge branch 'ps/refs-for-each'

Code refactoring around refs-for-each-* API functions.

* ps/refs-for-each:
  refs: replace `refs_for_each_fullref_in()`
  refs: replace `refs_for_each_namespaced_ref()`
  refs: replace `refs_for_each_glob_ref()`
  refs: replace `refs_for_each_glob_ref_in()`
  refs: replace `refs_for_each_rawref_in()`
  refs: replace `refs_for_each_rawref()`
  refs: replace `refs_for_each_ref_in()`
  refs: improve verification for-each-ref options
  refs: generalize `refs_for_each_fullref_in_prefixes()`
  refs: generalize `refs_for_each_namespaced_ref()`
  refs: speed up `refs_for_each_glob_ref_in()`
  refs: introduce `refs_for_each_ref_ext`
  refs: rename `each_ref_fn`
  refs: rename `do_for_each_ref_flags`
  refs: move `do_for_each_ref_flags` further up
  refs: move `refs_head_ref_namespaced()`
  refs: remove unused `refs_for_each_include_root_ref()`