Include merkleroot and client in signatures

<a href="https://github.com/maxtaco"><img src="https://avatars.githubusercontent.com/u/866815?v=3" align="left" width="96" height="96" hspace="10"></img></a> **Issue by [maxtaco](https://github.com/maxtaco)**
_Wednesday Dec 03, 2014 at 23:50 GMT_
_Originally opened as https://github.com/keybase/go-libkb/issues/62_

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Right now we left that out.
