Merge branch 'jk/for-each-ref-multi-key-sort-fix'

"git branch" and other "for-each-ref" variants accepted multiple
--sort=<key> options in the increasing order of precedence, but it
had a few breakages around "--ignore-case" handling, and tie-breaking
with the refname, which have been fixed.

* jk/for-each-ref-multi-key-sort-fix:
  ref-filter: apply fallback refname sort only after all user sorts
  ref-filter: apply --ignore-case to all sorting keys

diff --cc builtin/branch.c
Simple merge

diff --cc builtin/for-each-ref.c
Simple merge

diff --cc builtin/tag.c
Simple merge

diff --cc ref-filter.c
Simple merge

diff --cc ref-filter.h
Simple merge

diff --cc t/t6300-for-each-ref.sh
Simple merge