This is in preparation for moving the hashing to the frontend, which
requires us to handle the incoming data before passing it to the
backend's stream.
This flips rename detection around so instead of creating a
forward mapping from deltas to possible rename targets, instead
it creates a reverse mapping, looking at possible targets and
trying to find a source that they could have been renamed or
copied from. This is important because each output can only
have a single source, but a given source could map to multiple
outputs (in the form of COPIED records).
Additionally, this makes a couple of tweaks to the public rename
detection APIs, mostly renaming a couple of options that control
the behavior to make more sense and to be more like core Git.
I walked through the tests looking at the exact results and
updated the expectations based on what I saw. The new code is
different from the old because it cannot give some nonsense
results (like A was renamed to both B and C) which were part of
the outputs previously.
I frequently want to the the first N digits of an OID formatted
as a string and I'd like it to be efficient. This function makes
that easy and I could rewrite the OID formatters in terms of it.
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.
Previously a NULL oid was handled like an empty buffer and
returned a status empty string. This makes git_oid_tostr()
set the output buffer to the empty string instead.
