Markdown.Sanitizer.js should not use global window variable

```
We are trying to use Markdown.Sanitizer.js in Acre (a server-side javascript
environement).

However, we find ourselves hacking a window object to use Markdown.Sanitizer.js.

But if Markdown.Sanitizer.js passes "this" as the "window" variable, we can use
Markdown.Sanitizer.js on the server-side as is:

(function(window) {

...

})(this);

```

Original issue reported on code.google.com by `daep...@google.com` on 24 Sep 2012 at 2:59

Look at Markdown.Sanitizer.js in the repository to see how it currently references the global window variable. The change is to wrap the code in a function that takes 'this' as the window parameter, making it work in server-side environments like Acre. Test by checking if the script runs without a browser window object after the modification.

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