repack.usedeltabaseoffset config option now defaults to "true"

repack.usedeltabaseoffset config option now defaults to "true"

As announced for 1.6.0.

Access over the native protocol by old git versions is unaffected as
this capability is negociated by the protocol.  Otherwise setting this
config option to "false" and doing a 'git repack -a -d' is enough to
remain compatible with ancient git versions (older than 1.4.4).

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>