Function for_each_diff_pair 

pub fn for_each_diff_pair<B, C, F>(batch: &B, on_diff_pair: F)
where
    B: BatchReader<Time = C::Time> + Navigable<Cursor = C>,
    C: Cursor<Storage = B, Diff = Diff>,
    C::Time: Copy,
    C::ValOwn: 'static,
    F: FnMut(&<C::KeyContainer as BatchContainer>::Owned, C::Time, DiffPair<C::ValOwn>),

Walks batch and invokes on_diff_pair for each DiffPair at each (key, timestamp).

Thin wrapper around iter_diff_pairs.