Update code.google.com/p/go.crypto to the latest

Fixes LP 1312940, Fixes #43

This PR applies a branch from mgz (https://code.launchpad.net/~gz/juju-core/gosshnew_1312940). This branch was proposed a while ago but was delayed until all builders and package builders were running Go 1.2. 

Sinzui has confirmed that this has now happened so we are unblocked and can move off this old version of go.crypto.

This has the further effect that Go can be built from source without godeps, and this unblocks tools that consume Juju via `go get`, and makes us look like good Go citizens.