Merge branch 'sb/fmt-merge-msg'

* sb/fmt-merge-msg:
  fmt-merge-msg: hide summary option
  fmt-merge-msg: remove custom string_list implementation
  string-list: add unsorted_string_list_lookup()
  fmt-merge-msg: use pretty.c routines
  t6200: test fmt-merge-msg more
  t6200: modernize with test_tick
  fmt-merge-msg: be quiet if nothing to merge