Merge branch 'js/rebase-i-break'

"git rebase -i" learned a new insn, 'break', that the user can
insert in the to-do list.  Upon hitting it, the command returns
control back to the user.

* js/rebase-i-break:
  rebase -i: introduce the 'break' command
  rebase -i: clarify what happens on a failed `exec`

t/t3418-rebase-continue.sh

@@ -241,5 +241,14 @@ test_rerere_autoupdate -m
 GIT_SEQUENCE_EDITOR=: && export GIT_SEQUENCE_EDITOR
 test_rerere_autoupdate -i
 test_rerere_autoupdate --preserve-merges
+unset GIT_SEQUENCE_EDITOR
+
+test_expect_success 'the todo command "break" works' '
+	rm -f execed &&
+	FAKE_LINES="break exec_>execed" git rebase -i HEAD &&
+	test_path_is_missing execed &&
+	git rebase --continue &&
+	test_path_is_file execed
+'
 
 test_done