Windows Self-update

Makes Python updatable in the root environment in Windows.

The only known issue at this point is that the progress bars are not done correctly. Also, the subprocess causes the prompt to reappear, so you get weird stuff like seen in this image ("done" and the empty line was echoed by the batchfile, not typed by me).
![screenshot 2013-07-22 15 00 05](https://f.cloud.github.com/assets/71486/837568/56d7713e-f309-11e2-895a-af621676e8f8.png)