dht find connected peers

This PR extends the DHT to send information re: peer "connectedness".
This means that --upon resolving dht queries -- connected peers will
signal whether or not they are directly connected to the peer. this is
in preparation for mesh messaging, and our "STUN" for NAT traversal.
> I mean to call attention to the fact the this separate issue is the actual reason why one would begin to lose confidence in errors.

My point is that adding errors all over the place is bad practice itself. Look at the stdlib: https://gist.github.com/jbenet/9c20705c43a7ae47f9be  Programmer error that is _always_ incorrect, *should not ship*, should panic. We disagree on this and i dont think we'll reach consensus now.