git-rebase: don't ignore unexpected command line arguments

Currently, git-rebase will silently ignore any unexpected command-line switches and arguments (the command-line produced by git rev-parse). This allowed the rev-parse bug, fixed in the preceding commits, to go unnoticed. Let's make sure that doesn't happen again. We shouldn't be ignoring unexpected arguments. Let's not. Signed-off-by: Brandon Casey <drafnel@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>