Data Race

https://build.protocol-dev.com/job/race/9225/console

```
WARNING: DATA RACE
Read by goroutine 6:
github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream.(*Swarm).Conns()
/workspace/race/src/github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream/swarm.go:113 +0x81
github.com/jbenet/go-ipfs/net/swarm.(*Swarm).ConnectionsToPeer()
/workspace/race/src/github.com/jbenet/go-ipfs/net/swarm/swarm.go:119 +0x116
github.com/jbenet/go-ipfs/net/swarm.(*Swarm).NewStreamWithPeer()
/workspace/race/src/github.com/jbenet/go-ipfs/net/swarm/swarm.go:91 +0x125
github.com/jbenet/go-ipfs/net.(*network).NewStream()
/workspace/race/src/github.com/jbenet/go-ipfs/net/net.go:201 +0x9a
github.com/jbenet/go-ipfs/net/backpressure.TestStBackpressureStreamWrite()
/workspace/race/src/github.com/jbenet/go-ipfs/net/backpressure/backpressure_test.go:308 +0x886
testing.tRunner()
/usr/local/go/src/pkg/testing/testing.go:422 +0x10f

Previous write by goroutine 12:
runtime.mapassign1()
/usr/local/go/src/pkg/runtime/hashmap.goc:925 +0x0
github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream.func��002()
/workspace/race/src/github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream/conn.go:176 +0x55a
github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream.(*Swarm).addConn()
/workspace/race/src/github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream/conn.go:180 +0x236
github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream.(*Listener).accept()
/workspace/race/src/github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-peerstream/listener.go:98 +0x202
```