Changing the `add_outbound` function signature breaks the use in (this eunit test)[https://github.com/basho/riak_core/blob/7fc16113303b28b606eb68f07775e7c4a64247b6/src/riak_core_handoff_manager.erl#L612]. Not sure if that test even matters (it's conditionally guarded after all). But, figured I'd note the issue.