p5302: create repositories for index-pack results explicitly
Before
7176a314 (index-pack: complain when --stdin is used outside of a
repo) index-pack silently created a non-existing target directory; now
the command refuses to work unless it's used against a valid repository.
That causes p5302 to fail, which relies on the former behavior. Fix it
by setting up the destinations for its performance tests using git init.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>