Otherwise the created test repositories will be affected by users ~/.gitconfig.
For example, setting core.logAllrefupdates in users config will make all
calls to "git config --unset core.logAllrefupdates" fail which will break
the first test which uses the statement and expects it to succeed.
Signed-off-by: Alex Riesen <raa.lkml@gmail.com> Acked-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>