If the static url starts with /static/ then, the prefix /static/ is not ...

...removed because two // where added

I was having problems with the url http://localhost:8000/asset_proxy/?u=/static/filebrowser/uploadify/uploadify.swf which kept responding with 400. 

I checked out the ```static_proxy``` view was launching and exception at ```path = finders.find(url)``` in particular:

```
SuspiciousFileOperation: Attempted access to '//static/filebrowser/uploadify/uploadify.swf ' denied.
```

When I checked the view, it seems that if the url starts with /static/ then, it's not removed from the prefix, because after normalization it adds //, so you get ///static/.

Going back to what was before fixes the problem.