Informed of broken routes to self (split-horizon?)

[momerath42]

In my ilp-kit v4 test environment, of two peers, I'm seeing broken-route messages sent to the peer they pertain to. We should be preventing this for new_routes AND unreachable_through_me as part of a split-horizon policy (which I thought we had, in an ad-hoc form, at least for the new_routes side, in the logic surrounding adding routes and rebroadcasting them).