bundle: Use OFS_DELTA in bundle files

bundle: Use OFS_DELTA in bundle files

git-bundle first appeared in 2e0afafe ("Add git-bundle") in Feb 2007,
and first shipped in Git 1.5.1.

However, OFS_DELTA is an even earlier invention, coming about in
eb32d236 ("introduce delta objects with offset to base") in Sep 2006,
and first shipped in Git 1.4.4.5.

OFS_DELTA is smaller, about 3.2%-5% smaller, and is typically faster
to access than REF_DELTA because the exact location of the delta base
is available after parsing the object header.  Since all bundle aware
versions of Git are also OFS_DELTA aware, just make it the default.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>