[rdiff-backup-users] More windows patches

[Josh Nisly]

Here's another patch for rdiff-backup on Windows. os.popen does not work 
correctly on Windows, so this patch uses subprocess.Popen for windows 
platforms.

I've tried to work around the issue the patches showing up as text by 
tar'ing up the patch. Let me know if a different container format is 
preferred.

As always, I welcome any feedback.

Thanks,
JoshN

rdiff-backup-popen.tar
Description: Unix tar archive