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It's a patch, really. it's not the full multiconn fix.

This Commit changes the relationship between Conn and Swarm.
After this, Conn is significantly more autonomous, and follows
an interface.

From here, it will be very easy to make the MultiConn (that
handles multiple Conns per peer).

transition our use of the net package to multiaddr/net

and other logging switches. I kept the u.PErr and u.POut in cli
commands, as those do need to write raw output directly.