bump Go to 1.3

~~Requires #6539~~ merged
~~Requires #6684~~ merged
~~Requires #6913~~ merged
Requires #7170
Fixes #4983
Some cli integration tests are still failing with this branch.
@unclejack what do you think? @thaJeztah has a point, we could do `curl -sSL http://golang.org/dl/go1.3.src.tar.gz`.