Merge branch 'jc/for-each-ref'

* jc/for-each-ref:
  for-each-ref --format='%(flag)'
  for-each-ref --format='%(symref) %(symref:short)'
  builtin-for-each-ref.c: check if we need to peel onion while parsing the format
  builtin-for-each-ref.c: comment fixes