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* filtering InterfaceListenAddresses(s) instead
* return error if for loops skip
* large dial timeout

This adds two checks after a successful conn.Dial
* if the remote peer is not who we wanted, close conn
* if the remove peer is outselves, close conn

(the second is redundant, but the codebase may evolve to
end up disabling the first check, so keeping the second
in place helps)

note:
Loopback addresses are actually sent out (they _have to be_,
in cases where there are >1 node in the same machine), so
many times when trying connections, nodes end up dialing
themselves.

cc @whyrusleeping

Instead of erroring out, which would break the listener,
we instead log a message and continue. This is not an error,
the internet is a place with lots of probing + connection
failures.

This should handle early breakages, where a failing connection
would take out the listener entirely.

There are probably other errors we should be handling here,
like secure connection failures.

BenchmarkSign1B             1000           2406924 ns/op
BenchmarkSign10B            1000           2360527 ns/op
BenchmarkSign100B           1000           2354136 ns/op
BenchmarkSign1000B           500           2361775 ns/op
BenchmarkSign10000B          500           2415993 ns/op
BenchmarkSign100000B         500           2718051 ns/op
BenchmarkVerify1B          30000             52117 ns/op
BenchmarkVerify10B         30000             50968 ns/op
BenchmarkVerify100B        30000             51037 ns/op
BenchmarkVerify1000B       30000             56768 ns/op
BenchmarkVerify10000B      10000            105744 ns/op
BenchmarkVerify100000B      2000            628530 ns/op

not sure how it wasnt an error

This commit makes all network tests use ZeroLocalTCPAddress
as the initial peer address, and then relies on
net.ListenAddresses()

This should get rid of the tcp addr clash problems.

The separation of work in the p2p pkg is as follows:

- net implements the Swarm and connectivity
- protocol has muxer and header protocols
- host implements protocol muxing + services
- identify took over handshake completely! yay.
- p2p package works as a whole

using a placeholder net2 package so tests continue to pass.
Will be swapped atomically into main code.

remove comment about spdystream. this is now
superceded by go-peerstream interface.

The net package is the next to move. It will be massaged
a bit still to fix the Network / "NetworkBackend" conflict.

The crypto package moves into p2p. Nothing in it so far is ipfs
specific; everything is p2p-general.

I think it's time to move a lot of the peer-to-peer networking
but-not-ipfs-specific things into its own package: p2p.
This could in the future be split off into its own library.
The first thing to go is the peer.