[golang-dev] code review 6736069: runtime, syscall, os: add os.ExecPath() (string, error) (issue 6736069)

func executable() (string, error) {
f, err := Open("/proc/" + itoa(Getpid()) + "/text")
if err != nil {
return "", err
}
defer f.Close()
return syscall.Fd2path(int(f.Fd()))
}