[PATCHv2 0/4] refs.c: use transactions for the reflog

[Stefan Beller <sbeller@google.com>]

This is the core part of the refs-transactions-reflog series[1],
which was in discussion for a bit already.

The idea is to have the reflog being part of the transactions, which
the refs are already using, so the we're moving towards a database
like API in the long run. This makes git easier to maintain as well
as opening the possibility to replace the backend with a real database.

The first patch is essentially just some sed magic with reformatting
the code, so the naming convention fits better, because the transactions
will handle both the refs as well as the reflog after this series.

The second patch is also just a rename patch.

The meat and most of the lines of code are found in the 3rd patch.
It was completely rewritten from scratch using ideas provided by
Jonathan, thanks! We'll treat the refs and reflogs a bit differently
within the transaction updates data structure, as the hard part for
the refs is during the commit phase, while the hard part for the reflogs
is during the preparation phase now.

We're using a temporary file for creating the new reflog and rename it
into place afterwards utilizing the lock file API.

The last patch makes actually use of the reflog transaction API.

Any comments would be appreciated,
Thanks,
Stefan