Do not retain a reference to the refname passed to the each_ref_fn
callback get_name(), because there is no guarantee of the lifetimes of
these names.  Instead, make a local copy when needed.
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>