t3400: demonstrate failure with format.useAutoBase

t3400: demonstrate failure with format.useAutoBase

Ever since bb52995f3e (format-patch: introduce format.useAutoBase
configuration, 2016-04-26), `git rebase` has been broken when
`format.useAutoBase = true`. It fails when rebasing a branch:

	fatal: failed to get upstream, if you want to record base commit automatically,
	please use git branch --set-upstream-to to track a remote branch.
	Or you could specify base commit by --base=<base-commit-id> manually
	error:
	git encountered an error while preparing the patches to replay
	these revisions:

	    ede2467cdedc63784887b587a61c36b7850ebfac..d8f581194799ae29bf5fa72a98cbae98a1198b12

	As a result, git cannot rebase them.

Demonstrate that failure here.

Reported-by: Christian Biesinger <cbiesinger@google.com>
Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>