This adds more tests for 'reflog delete' and marks it as
broken, as currently a call to 'git reflog delete HEAD@{1}'
deletes entries in the currently checked out branch's log,
not the HEAD log.
Noticed by John Wiegley
Signed-off-by: Pieter de Bie <pdebie@ai.rug.nl> Signed-off-by: Junio C Hamano <gitster@pobox.com>