core.fsync: use batch mode and sync loose objects by default on Windows

core.fsync: use batch mode and sync loose objects by default on Windows

Git for Windows has defaulted to core.fsyncObjectFiles=true since
September 2017. We turn on syncing of loose object files with batch mode
in upstream Git so that we can get broad coverage of the new code
upstream.

We don't actually do fsyncs in the most of the test suite, since
GIT_TEST_FSYNC is set to 0. However, we do exercise all of the
surrounding batch mode code since GIT_TEST_FSYNC merely makes the
maybe_fsync wrapper always appear to succeed.

Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>