merge unpack-objects to index-pack?

Hi,

I'm looking at adding large file support to unpack-objects. A simple way is just to stream large blobs into loose large blobs. But I'd rather keep those blobs in pack because pack-objects is happier that way. I'm looking at unpack-objects and thinking maybe it's best to just merge it back to index-pack.

In normal mode (all small objects), index-pack receives the pack stream. Objects will be unpacked in phase two, resolving objects in index-pack. The only downside I can see is the new unpack-objects now write temporary pack on disk, which does not sound too bad to me. unpack-packs is called on small packs so extra space is small. For single-huge-blob packs, it's good to keep them on disk anyway. When the pack has large blobs, we could either just keep full pack.

After this, the only pack receiver at client side is index-pack. fetch-pack does not have to choose between unpack-objects and index-pack, just pass --unpack-limit <n> to index-pack.

What do you think?