goflymake currently succeeds even if go build/go test fail. This seems to cause the version of flymake on my home system to ignore the goflymake output and assume there are no errors.
propagate go tool failure
On closer inspection, my home flymake wasn't checking the error code, I just had a bad process environment in my mac emacs. So this change doesn't fix anything (but it still seems like not a bad idea to me).