Enable ofs-delta during send-pack/receive-pack protocol

Enable ofs-delta during send-pack/receive-pack protocol

In "allow OFS_DELTA objects during a push" Nicolas Pitre taught C
git how to enable OBJ_OFS_DELTA usage in a pack file created on a
client, to be processed by receive-pack on the server side.

This creates a smaller pack file during transfer, as the OFS_DELTA
format uses less per-delta header space than the classical REF_DELTA.
If the receiving peer is going to just store the pack to disk,
this would also produce a smaller on-disk pack file.

In his change, Nico tied the server side enablement of the capability
to the server's repack.usedeltabaseoffset setting, which can be
set to false in a repository that needs to service direct access
clients that are old to understand OFS_DELTA.  We do the same here
in JGit to match semantics.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>