Merge branch 'mh/rebase-fixup' (early part)

* 'mh/rebase-fixup' (early part):
  rebase-i: Ignore comments and blank lines in peek_next_command
  lib-rebase: Allow comments and blank lines to be added to the rebase script
  lib-rebase: Provide clearer debugging info about what the editor did
  Add a command "fixup" to rebase --interactive
  t3404: Use test_commit to set up test repository

diff --cc git-rebase--interactive.sh
Simple merge