Rather than having separate write_ref calls, make clients start a
transaction, add some refs, and then commit it. While this doesn't
make it 100% atomic, it makes it easier for us to use an atomic
model, and it means we don't do as much I/O updating the summary
file and such.
https://bugzilla.gnome.org/show_bug.cgi?id=707644
An earlier version of this API acted like git in that some objects
would be staged in a temporary directory which would be then committed
in one go by moving files around. The API doesn't match most users
expectations though, as while the stage is nice as a high-level API
it isn't really suited for low-level APIs.
While the stage was removed, the APIs were never renamed. Rename
them now so that they match expectations.
https://bugzilla.gnome.org/show_bug.cgi?id=707644