Currently 'go install -a' fails when run for packages under GOPATH, if the GOROOT is not
writeable:
$ sudo tar -C /usr/local -xzf go1.0.3.linux-amd64.tar.gz
$ echo $GOPATH
/home/jsing/src/mygo
$ go install -a example
go install runtime: open /usr/local/go/pkg/linux_amd64/runtime.a: permission denied
Obviously '-a' means all, however it would be useful if we could force a rebuild for all
of the dependencies under the GOPATH only (or skip dependencies in GOROOT).