"git interpret-trailers" learned to properly handle the
"Conflicts:" block at the end.

* cc/interpret-trailers-more:
  trailer: add test with an old style conflict block
  trailer: reuse ignore_non_trailer() to ignore conflict lines
  commit: make ignore_non_trailer() non static
  merge & sequencer: turn "Conflicts:" hint into a comment
  builtin/commit.c: extract ignore_non_trailer() helper function
  merge & sequencer: unify codepaths that write "Conflicts:" hint
  builtin/merge.c: drop a parameter that is never used