handshake: error out while sending + dbg
ping: return sme msg

This fixes the broken pinging. (the issue was the cluster
level, it's bein set incorrectly (off by one))

Anyway, this works now:

    [peer: QmfQTbC3LxfpK5WoyHW2WgnAzo6d6GePuq2wHTsJNXM5PS] Sent message type: 'PING' [to = QmNXUeFrV9gxR4aqJddEsfhWZLSJrUsfpUSeRb3R7xvSp9]
    [QmfQTbC3LxfpK5WoyHW2WgnAzo6d6GePuq2wHTsJNXM5PS] ping QmNXUeFrV9gxR4aqJddEsfhWZLSJrUsfpUSeRb3R7xvSp9 end (err = %!s(<nil>))

cc @whyrusleeping
Merge pull request #104 from jbenet/feat/fix-ping

Fixed Ping (minor)