All the tests so far check that @{N} is the same as HEAD@{N} (for
positive N). However, this is not always the case; write a couple of
tests for this.
[fc: simplify some wording]
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com> Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>