Sending os.Interrupt via os.Process.Signal works on most platforms, but doesn't work on
Windows. There is a TODO(rsc) to do it. Someone should do it for Go 1.3:

https://code.google.com/p/go/source/browse/src/pkg/os/exec_windows.go?name=go1.2rc3#62

func (p *Process) signal(sig Signal) error {
        if p.done() {
                return errors.New("os: process already finished")
        }
        if sig == Kill {
                return terminateProcess(p.Pid, 1)
        }
        // TODO(rsc): Handle Interrupt too?
        return syscall.Errno(syscall.EWINDOWS)
}