The frontend used to look at the file directly, but that's obviously not
the right thing to do. Expose it on the backend and use that function
instead.
Whenever a reference is created or updated, we need to write to the
reflog regardless of whether the user gave us a message, so we shouldn't
leave that to the ref frontend, but integrate it into the backend.
This also eliminates the race between ref update and writing to the
reflog, as we protect the reflog with the ref lock.
As an additional benefit, this reflog append on the backend happens by
appending to the file instead of parsing and rewriting it.
References and their logs are logically coupled, let's make it so in
the code by moving the fs-based reflog implementation to live next to
the fs-based refs one.
As part of the change, make the function take names rather than
references, as only the names are relevant when looking up and
handling reflogs.
Nobody should ever be using anything other than ALL at this level, so
remove the option altogether.
As part of this, git_reference_foreach_glob is now implemented in the
frontend using an iterator. Backends will later regain the ability of
doing the glob filtering in the backend.
