This moves some of the odb_backend stuff that is related to the
internals of an odb_backend implementation into include/git2/sys.
Some of the stuff related to streaming I left in include/git2
because it seemed like it would be reasonably needed by a normal
user who wanted to stream objects into and out of the ODB.
Also, I added APIs for traversing the list of backends so that
some of the tests would not need to access ODB internals.
This was the first implementation and its goal was simply to have
something that worked. It is slow and now it's just taking up
space. Remove it and switch the one known usage to use the streaming
indexer.
It's not really needed with the current code as we have EOS and the
sideband's flush to tell us we're done.
Keep the distinction between processed and received objects.
Trying to send every single line immediately won't give us any speed
improvement and duplicates the code we need for other transports. Make
the git transport use the same buffer functions as HTTP.
This will allow us to index a packfile as soon as we receive it from
the network as well as storing it with its final name so we don't need
to pass temporary file names around.
1. The license header is technically not valid if it doesn't have a
copyright signature.
2. The COPYING file has been updated with the different licenses used in
the project.
3. The full GPLv2 header in each file annoys me.
