Merge branch 'js/advise-when-skipping-cherry-picked'

"git rebase" by default skips changes that are equivalent to
commits that are already in the history the branch is rebased onto;
give messages when this happens to let the users be aware of
skipped commits, and also teach them how to tell "rebase" to keep
duplicated changes.

* js/advise-when-skipping-cherry-picked:
  sequencer: advise if skipping cherry-picked commit

diff --cc Documentation/git-rebase.txt
Simple merge

diff --cc advice.c
Simple merge

diff --cc advice.h
Simple merge

diff --cc builtin/rebase.c
Simple merge

diff --cc sequencer.c
Simple merge