rebase: add options passed to git-am

Add the options --committer-date-is-author-date and --ignore-date
to git-rebase. They were introduced in commit a79ec62d0 for git-am.
These options imply --force-rebase.

Signed-off-by: Michele Ballabio <barra_cuda@katamail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -309,6 +309,10 @@ do
 			;;
 		esac
 		;;
+	--committer-date-is-author-date|--ignore-date)
+		git_am_opt="$git_am_opt $1"
+		force_rebase=t
+		;;
 	-C*)
 		git_am_opt="$git_am_opt $1"
 		;;