Windows missing conversion

```
In mmap_windows.go line 26:

h, err := syscall.CreateFileMapping(f.Fd(), nil, ...

Need convert to syscall.Handle:

h, err := syscall.CreateFileMapping(syscall.Handle(f.Fd()), nil,
```

Original issue reported on code.google.com by `daniel.p...@gmail.com` on 6 Nov 2013 at 5:17
