Sort AAE differences before acting upon them via read-repair

            %% Sort the keys.  For vnodes that use backends that preserve
            %% lexicographic sort order for BKeys, this is a big
            %% improvement.  For backends that do not, e.g. Bitcask, sorting
            %% by BKey is unlikely to be any worse.  For Riak CS's use
            %% pattern, sorting may have some benefit since block N is
            %% likely to be adjacent on disk to block N+1.