5723fe7 (Avoid cross-directory renames and linking on object creation,
2008-06-14) changed the call to use link() directly instead of through a
custom wrapper, but forgot that it returns 0 or -1, not 0 or errno.
Signed-off-by: Thomas Rast <trast@student.ethz.ch> Signed-off-by: Junio C Hamano <gitster@pobox.com>