[go-nuts] command.Process.Kill() results in an invalid exit status code

I might be missing something (probably something Deep and True about how
unix processes and signals work) but:

```
package main

import (
"fmt"
"os/exec"
"syscall"
)

func main() {
cmd := exec.Command("sleep", "1000000")
cmd.Start()

done := make(chan struct{})
go func() {
err := cmd.Wait()
exitStatus := cmd.ProcessState.Sys().(syscall.WaitStatus).ExitStatus()

fmt.Println("Error:", err)
fmt.Println("Status:", exitStatus)

close(done)
}()

cmd.Process.Kill()

<-done
}
```

Outputs:
Error: signal: killed
Status: -1

Looking at ExitStatus here
(http://golang.org/src/pkg/syscall/syscall_linux.go?s=4510:4546#L180) I see
that -1 implies the process has not exited. But it actually has (I checked
with `ps`)!

Is this a bug, or desired behavior? When I run `sleep 1000000` in a shell
and then send said process the KILL signal I get an exit code of 137 which
is consistent with http://www.tldp.org/LDP/abs/html/exitcodes.html

Thanks!

Onsi