Recognize when the reference has changed since we loaded it.

We don't actually pass the old value yet.

We will reuse this later for deletion.

Bring the race detection goodness to symbolic references as well.

Add a parameter to the backend to allow checking for the old symbolic
target.

Free the old ref even on success.

In case we loose the race to update the reference, return GIT_EMODIFIED
to let the user distinguish it from other types of errors.

Change the name to _matching() intead of _if(), and force _set_target()
to be a conditional update. If the user doesn't care about the old
value, they should use git_reference_create().

Allow updating references if the old value matches the given one.

Corrections for merge working directory validation

Validating the workdir should not compare HEAD to working
directory - this is both inefficient (as it ignores the cache)
and incorrect.  If we had legitimately allowed changes in the
index (identical to the merge result) then comparing HEAD to
workdir would reject these changes as different.  Further, this
will identify files that were filtered strangely as modified,
while testing with the cache would prevent this.

Also, it's stupid slow.

Correct "new" id for reattached-HEAD reflog entry

Add `git_reference_is_note`.

Update to latest clar

Reflog completionism