Earlier we disabled threading when online_cpus() said "1", but on a
filesystem with long latency (or in a cold cache situation), using
multiple threads to drive I/O in parallel would improve performance
even on a single-core machines.
Signed-off-by: Victor Leschuk <vleschuk@accesssoftek.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>