rebase -i -p: Fix --continue after a merge could not be redone

When a merge that has a conflict was rebased, then rebase stopped to let
the user resolve the conflicts. However, thereafter --continue failed
because the author-script was not saved. (This is rebase -i's way to
preserve a commit's authorship.) This fixes it by doing taking the same
failure route after a merge that is also taken after a normal cherry-pick.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase--interactive.sh

@@ -256,9 +256,8 @@ pick_one_preserving_merges () {
 				output git merge $STRATEGY -m "$msg" \
 					$new_parents
 			then
-				git rerere
 				printf "%s\n" "$msg" > "$GIT_DIR"/MERGE_MSG
-				die Error redoing merge $sha1
+				die_with_patch $sha1 "Error redoing merge $sha1"
 			fi
 			;;
 		*)

t/t3409-rebase-preserve-merges.sh

@@ -75,7 +75,7 @@ test_expect_success 'rebase -p fakes interactive rebase' '
 	)
 '
 
-test_expect_failure '--continue works after a conflict' '
+test_expect_success '--continue works after a conflict' '
 	(
 	cd clone2 &&
 	git fetch &&