Files loaded though custom VirtualPathProvider not found

Hi!

I use a custom VirtualPathProvider (http://nuget.org/List/Packages/EmbeddedResourceVirtualPathProvider) to load resources from assemblies. They don't seem to be picked up.

I suspect that Cassette looks to see if files exist inside the web folder using the filesystem rather than
```System.Web.Hosting.HostingEnvironment.VirtualPathProvider.FileExists(string virtualPath);

``````
and content should be loaded via:
```var stream = HostingEnvironment.VirtualPathProvider.OpenFile(file);
var text = new StreamReader(stream).ReadToEnd();
``````

I had a very quick look at the source but am not sure how to patch it exactly. Apologies if I'm wrong about this and it's something else I'm doing that is preventing my code from working!