Merge branch 'sb/sequencer-abort-safety' into maint

Merge branch 'sb/sequencer-abort-safety' into maint

Unlike "git am --abort", "git cherry-pick --abort" moved HEAD back
to where cherry-pick started while picking multiple changes, when
the cherry-pick stopped to ask for help from the user, and the user
did "git reset --hard" to a different commit in order to re-attempt
the operation.

* sb/sequencer-abort-safety:
  Revert "sequencer: remove useless get_dir() function"
  sequencer: remove useless get_dir() function
  sequencer: make sequencer abort safer
  t3510: test that cherry-pick --abort does not unsafely change HEAD
  am: change safe_to_abort()'s not rewinding error into a warning
  am: fix filename in safe_to_abort() error message