Upgrade golang package to 1.2.2

This takes the Ubuntu Trusty packaging for 1.2.1, backports it to Precise, and bumps the version to 1.2.2.

Updating should not cause any issues for existing code because of the [promise of compatibility](http://golang.org/doc/go1compat) that Go gives for all 1.x releases.

This release brings some new features that are useful to us:
* performance improvements (including a 30% boost for JSON encoding)
* `go get -t` option to simplify fetching test dependencies.
* test coverage tool

Full release notes: http://golang.org/doc/go1.2