Improvements to the shellscripts

* Added "go.sh" which runs a 'go' subcommand with the right GOPATH.
* test.sh: Ignore "unreachable code" warning from "go vet"
  (It's from some panic() calls that were added deliberately to appease
  the 1.0.3 compiler, but which will cause this warning from go vet in
  1.1.)