add tests for rebasing with patch-equivalence present

Signed-off-by: Martin von Zweigbergk <martinvonz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-rebase.sh

@@ -81,3 +81,20 @@ reset_rebase () {
 	git reset --hard &&
 	git clean -f
 }
+
+cherry_pick () {
+	git cherry-pick -n "$2" &&
+	git commit -m "$1" &&
+	git tag "$1"
+}
+
+revert () {
+	git revert -n "$2" &&
+	git commit -m "$1" &&
+	git tag "$1"
+}
+
+make_empty () {
+	git commit --allow-empty -m "$1" &&
+	git tag "$1"
+}