If we leave a detached head, exactly one of two things happens: either
checkout warns about it being an orphan or describes it as a courtesy.
Test t2020 already checked that the warning is shown as needed. This
patch also checks for the description.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>